How can probiotics and prebiotics help you? What the research says

Probiotics are living microorganisms that provide a health benefit, and prebiotics are fibers that feed these friendly bacteria, mostly in your gut. These therapies, found in certain foods or as supplements, can manage gastrointestinal symptoms and some body terrainthe internal conditions of your body, including nutritional status, fitness, blood sugar balance, hormone balance, inflammation and more factors common in cancer, and they may lead to better recovery from surgery.

How can probiotics and prebiotics help you? What the research says

We summarize the clinical evidence for each medical benefit here. We begin with our assessment of the strength of evidence within each category, followed by a brief summary of individual studies or reviews of several studies. In assessing the strength of evidence, we consider the study design, number of participants, and the size of the treatment effect (how much outcomes changed with treatment).

To see more details, click the plus sign to the right of any section.

Our assessments of evidence for each medical benefit fall into one of these categories:

Strong evidence: consistent, significant effects in several large (or at least one very large) well designed clinical studies or at least two meta-analysesa statistical analysis that combines the results of two or more research studies; the results of smaller research studies addressing the same or similar questions can be analyzed as though they are one bigger, more powerful study of clinical studies of moderate or better quality (or one large meta-analysis) finding similar results
Good evidence: significant effects in one large or several mid-sized and well-designed clinical studies ( randomized controlled trialsa study design in which people are randomly assigned to either an experimental group or a control group to compare the outcomes from different treatments; an RCT is considered a strong design for determining a therapy’s effects with an appropriate placebo or other strong comparison control or observational studies that control for confounds)
Modest evidence: significant effects in at least three small but well-designed randomized controlled trials (RCTs), or one or more well-designed, mid-sized clinical studies of reasonably good quality (RCTs or observationala type of study in which individuals are observed or certain outcomes are measured, but no attempt is made to affect the outcome (for example, no treatment is given); an example is a study that records people’s diets, but doesn’t try to alter their diets, and looks for patterns of disease or other outcomes related to different foods studies), or several small studies aggregated into a meta-analysis
Preliminary evidence: significant effects in small or poorly designed clinical studies OR conflicting results in adequate studies but a preponderance of evidence of an effect
Weak evidence: one or more case studies, supported by animal evidence OR small treatment effects of limited clinical significance OR studies with no controls OR weak trends of effects
Insufficient evidence: preclinical evidence only OR clinical studies with such poor or unclear methodology that no conclusion can be drawn OR conflicting findings across clinical studies with no preponderance of evidence in one direction; conflicting evidence occurs when studies find conflicting effects (positive effect vs no effect or negative effect) with the same treatment and the same general study population (same cancer type, for example)

Learn more about how we research and rate therapies and practices in How We Rate Therapies ›

The most-studied and commonly used organisms in probiotic preparations are lactobacilli and bifidobacteria,¹Power SE, O’Toole PW, Stanton C, Ross RP, Fitzgerald GF. Intestinal microbiota, diet and health. British Journal of Nutrition. 2014 Feb;111(3):387-402. although many other organisms have been studied. Differences in which specific probiotics are used may contribute to conflicting findings across studies.

Some evidence shows that individuals respond differently to probiotics, with some people being sensitive and others resistant to colonization by the species in a probiotic treatment. Diet directly impacts the composition of your microbiome, and so both your diet and the existing composition of your microbiome may influence your sensitivity to probiotics.²Zmora N, Zilberman-Schapira G et al. Personalized gut mucosal colonization resistance to empiric probiotics is associated with unique host and microbiome features. Cell. 2018 Sep 6;174(6):1388-1405.e21.

Your Microbiome

Careful attention to the details of studies may help you determine whether you (or your patients) are likely to benefit from the treatments described.

Improving treatment outcomes

Are probiotics and prebiotics linked to improved survival? Are they linked to less cancer growth or metastasis? Do they enhance the anticancer action of other treatments or therapies? We present the evidence.

Advanced cancer

Modest evidencesignificant effects in at least three small but well-designed randomized controlled trials (RCTs), or one or more well-designed, mid-sized clinical studies of reasonably good quality (RCTs or observational studies), or several small studies aggregated into a meta-analysis (this is the CancerChoices definition; other researchers and studies may define this differently) of longer progression-free survival among people with advanced kidney or lung cancers undergoing immune checkpoint inhibitor treatment also treated with probiotics

Substantially longer progression-free survival and a weak trend toward a higher response rate among people with intermediate- or poor-risk metastatic renal cell carcinoma and no prior systemic therapy (no checkpoint inhibitor therapy) treated with daily oral CBM588, a bifidogenic live bacterial product, in addition to nivolumab and ipilimumab compared to nivolumab and ipilimumab alone in a small RCTrandomized controlled trial, a study design in which people are randomly assigned to either an experimental group or a control group to compare the outcomes from different treatments; an RCT is considered a strong design for determining a therapy’s effects³Dizman N, Meza L et al. Nivolumab plus ipilimumab with or without live bacterial supplementation in metastatic renal cell carcinoma: a randomized phase 1 trial. Nature Medicine. 2022 Apr;28(4):704-712.
Longer progression-free survival and overall survival among people with advanced non-small cell lung cancer undergoing immune checkpoint inhibitor treatment also treated with probiotic Clostridium butyricum therapy compared to no probiotics in a mid-sized observationala type of study in which individuals are observed or certain outcomes are measured, but no attempt is made to affect the outcome (for example, no treatment is given); an example is a study that records people’s diets, but doesn’t try to alter their diets, and looks for patterns of disease or other outcomes related to different foods study⁴Tomita Y, Ikeda T et al. Association of probiotic Clostridium butyricum therapy with survival and response to immune checkpoint blockade in patients with lung cancer. Cancer Immunology Research. 2020 Oct;8(10):1236-1242.
Longer progression-free survival and better disease control and overall response, but no evidence of an effect on overall survival, among people with advanced or recurrent non-small cell lung cancer undergoing antiprogrammed cell death-1 (PD-1) therapy also treated with probiotics compared to no probiotics in a mid-sized observational study⁵Takada K, Shimokawa M et al. Clinical impact of probiotics on the efficacy of anti-PD-1 monotherapy in patients with nonsmall cell lung cancer: a multicenter retrospective survival analysis study with inverse probability of treatment weighting. International Journal of Cancer. 2021 Jul 15;149(2):473-482.

Probiotics combined with other therapies

Weak evidenceone or more case studies, supported by animal evidence OR small treatment effects of limited clinical significance OR studies with no controls OR weak trends of effects (this is the CancerChoices definition; other researchers and studies may define this differently) of complete remission in a single person with high grade, non-muscle involved bladder cancer refractory to Bacillus Calmette-Guerin treated with intravenous pharmacological ascorbate and subcutaneous mistletoe along with several supplements

Weak evidence of good health and wellness among people with cancer treated with probiotics, intravenous vitamin C, and other supplements and medications

Probiotics, mistletoe, pharmacological ascorbate, and several supplements: weak evidence of complete remission in a single person with high grade, non-muscle involved bladder cancer refractory to Bacillus Calmette-Guerin treated with intravenous pharmacological ascorbate and subcutaneous mistletoe along with several supplements

Complete remission (no evidence of disease) in a nonsmoking woman with high grade, non-muscle involved bladder cancer (carcinoma in situ) refractory to Bacillus Calmette-Guerin treated with intravenous pharmacological ascorbate and subcutaneous mistletoe 3 times a week, and also intravenous and intravesical mistletoe once a week for an 8-week induction treatment using a dose-escalation protocol and then maintenance therapy of the same protocol for 3 weeks every 3 months for 2 years; plus the supplements below in a case studya descriptive and exploratory analysis of a person, group, or event regarding changes observed over time; because changes due to treatment are not compared to similar changes over time without treatment, a case study is considered a weak study design:⁶Davis D, Seely D et al. Complete remission of BCG-refractory high-grade bladder CIS with pharmacologic ascorbate and mistletoe. Alternative Therapies in Health and Medicine. 2023 May;29(4):6-17.
- Daily: turmeric, vitamin D, omega-3 fatty acids, coenzyme Q10, chaga mushroom, and melatonin at night
- During induction: probiotics
- During maintenance: probiotics, melatonin 4 times a day, and a fiber supplement made of flaxseed, probiotics, and L-glutamine

Probiotics with intravenous vitamin C and other supplements and medications: weak evidence of good health and wellness with no symptoms of metastasis or recurrence 9 years after diagnosis in a person with bladder cancer treated with probiotics, intravenous vitamin C, and other supplements

Good health with no symptoms of metastasis or recurrence 9 years after diagnosis in a man with a primary bladder tumor treated with 30 g intravenous vitamin C twice per week for 3 months, followed by 30 g once every 1–2 months for 4 years, along with botanical extract, chondroitin sulfate, chromium picolinate, flax oil, glucosamine sulfate, α-lipoic acid, Lactobacillus acidophilus, L. rhamnosus and selenium in a case study⁷Padayatty SJ, Riordan HD et al. Intravenously administered vitamin C as cancer therapy: three cases. Canadian Medical Association Journal. 2006;174(7):937-42.

Optimizing your body terrain

Do probiotics and prebiotics promote an environment within your body that is less supportive of cancer development, growth, or spread? We present the evidence.

See Optimizing Your Body Terrain ›

Find medical professionals who specialize in managing body terrain factors: Finding Integrative Oncologists and Other Practitioners ›

Body weight

No evidence of an effectoverall, one or more studies did not demonstrate that a treatment or intervention led to an expected outcome; this does not always mean that there is no effect in clinical practice, but that the studies may have been underpowered (too few participants) or poorly designed. Larger, well-designed studies provide more confidence in making assessments. on measures of body weight among adults with metabolic syndrome treated with various strains of probiotics or synbiotics in a combined analysis of studies

Weak evidenceone or more case studies, supported by animal evidence OR small treatment effects of limited clinical significance OR studies with no controls OR weak trends of effects (this is the CancerChoices definition; other researchers and studies may define this differently) of lower measures of body weight among overweight or obese and insulin-resistant people treated with pasteurized Akkermansia muciniphila

Preliminary evidencesignificant effects in small or poorly designed clinical studies OR conflicting results in adequate studies but a preponderance of evidence of an effect (this is the CancerChoices definition; other researchers and studies may define this differently) of lower measures of body weight among women with polycystic ovarian syndrome treated with synbiotics

Preliminary evidence of more excess weight loss after for gastric surgery for morbid obesity among people treated with a probiotic

No evidence of an effect on measures of body weight or composition among overweight, obese, or prediabetic people treated with prebiotics in 2 small studies

Probiotics or synbiotics

No evidence of an effect on measures of body weight among adults with metabolic syndrome treated with various strains of probiotics or synbiotics in a combined analysis of studies

Weak evidence of lower measures of body weight among overweight or obese and insulin-resistant people treated with pasteurized Akkermansia muciniphila

Preliminary evidence of lower measures of body weight among women with polycystic ovarian syndrome treated with synbiotics

Preliminary evidence of more excess weight loss after for gastric surgery for morbid obesity among people treated with a probiotic

No evidence of an effect on body weight, body mass index, or waist circumference among adults with metabolic syndrome treated with various strains of probiotics or synbiotics in a meta-analysisa statistical analysis that combines the results of two or more research studies; the results of smaller research studies addressing the same or similar questions can be analyzed as though they are one bigger, more powerful study of 9 RCTsrandomized controlled trial, a study design in which people are randomly assigned to either an experimental group or a control group to compare the outcomes from different treatments; an RCT is considered a strong design for determining a therapy’s effects⁸Hadi A, Arab A et al. Effects of probiotic supplementation on anthropometric and metabolic characteristics in adults with metabolic syndrome: a systematic review and meta-analysis of randomized clinical trials. Clinical Nutrition. 2021 Jun 8;40(7):4662-4673.
Weak trends toward lower body weight, fat mass, and hip circumference among overweight or obese and insulin-resistant people treated with pasteurized Akkermansia muciniphila for 3 months compared to placeboa pill, medicine, or procedure—thought to be both harmless and ineffective—prescribed for the psychological benefit to the patient or as a sham treatment in a study to allow a comparison to a therapy of interest in a small RCT⁹Depommier C, Everard A et al. Supplementation with Akkermansia muciniphila in overweight and obese human volunteers: a proof-of-concept exploratory study. Nature Medicine. 2019 Jul;25(7):1096-1103.
Lower body mass index, weight, and waist circumference among women with polycystic ovarian syndrome treated with synbiotics compared to placebo in a small RCT¹⁰Esmaeilinezhad Z, Babajafari S et al. Effect of synbiotic pomegranate juice on glycemic, sex hormone profile and anthropometric indices in PCOS: a randomized, triple blind, controlled trial. Nutrition, Metabolism & Cardiovascular Diseases. 2019 Feb;29(2):201-208.
No evidence of an effect on body weight among obese, prediabetic but otherwise generally healthy adults participating in intermittent fasting and taking a daily probiotic capsule compared to placebo for 12 weeks in a small RCT¹¹Tay A, Pringle H, Penning E, Plank LD, Murphy R. PROFAST: a randomized trial assessing the effects of intermittent fasting and Lacticaseibacillus rhamnosus probiotic among people with prediabetes. Nutrients. 2020 Nov 17;12(11):3530.
More weight loss after Roux-en-Y gastric bypass surgery for morbid obesity among people treated with Lactobacillus after surgery compared to controls in a small RCT¹²Woodard GA, Encarnacion B et al. Probiotics improve outcomes after Roux-en-Y gastric bypass surgery: a prospective randomized trial. Journal of Gastrointestinal Surgery. 2009 Jul;13(7):1198-204.
Less abdominal visceral and subcutaneous fat and lower body weight among adults with obese tendencies treated with fermented milk containing LG2055 compared to baseline, while no reductions were found among people drinking fermented milk without LG2055 in a small comparison trial¹³Kadooka Y, Sato M et al. Regulation of abdominal adiposity by probiotics (Lactobacillus gasseri SBT2055) in adults with obese tendencies in a randomized controlled trial. European Journal of Clinical Nutrition. 2010 Jun;64(6):636-43.

Prebiotics only: no evidence of an effect on measures of body weight or composition among overweight, obese, or prediabetic people treated with prebiotics in 2 small studies

No evidence of an effect on body composition among overweight or obese (body mass index 28-40), prediabetic men and women treated with galacto-oligosaccharides for 12 weeks compared to placebo (maltodextrin) in a small RCT¹⁴Canfora EE, van der Beek CM et al. Supplementation of diet with galacto-oligosaccharides increases bifidobacteria, but not insulin sensitivity, in obese prediabetic individuals. Gastroenterology. 2017 Jul;153(1):87-97.e3.
No evidence of an effect on body weight, body mass index, percentage of fat, and percentage of trunk fat among prediabetic people treated with xylooligosaccharide prebiotics for 8 weeks compared to placebo in a small RCT¹⁵Yang J, Summanen PH et al. Xylooligosaccharide supplementation alters gut bacteria in both healthy and prediabetic adults: a pilot study. Frontiers in Physiology. 2015 Aug 7;6:216.

High blood sugar and insulin resistance

Good evidencesignificant effects in one large or several mid-sized and well-designed clinical studies (randomized controlled trials (RCTs) with an appropriate placebo or other strong comparison control or observational studies that control for confounds) (this is the CancerChoices definition; other researchers and studies may define this differently) of lower fasting blood glucose and insulin levels and a weak trendan apparent change due to a therapy, close to but not achieving full statistical significance (this is the CancerChoices definition; other researchers and studies may define this differently toward lower blood sugar among people with type 1 or 2 diabetes or prediabetes treated with probiotic, prebiotic, or synbiotic supplementation

Insufficient (conflicting) evidencepreclinical evidence only OR clinical studies with such poor or unclear methodology that no conclusion can be drawn OR conflicting findings across clinical studies with no preponderance of evidence in one direction; conflicting evidence occurs when studies find conflicting effects (positive effect vs no effect or negative effect) with the same treatment and the same general study population (same cancer type, for example) (this is the CancerChoices definition; other researchers and studies may define this differently) of an effect on fasting blood sugar, insulin resistancea condition in which cells in your muscles, fat, and liver don’t respond well to insulin and can’t efficiently take up glucose from your blood for energy, or insulin among adults with metabolic syndrome or metabolic disorders treated with probiotics or synbiotics

No evidence of an effect on insulin levels, blood sugar, fasting plasma glucose, insulin resistance, or insulin-like growth factor-1 among postmenopausal, overweight, and obese women with hormone receptor-positive breast cancer treated with a synbiotic

Modest evidencesignificant effects in at least three small but well-designed randomized controlled trials (RCTs), or one or more well-designed, mid-sized clinical studies of reasonably good quality (RCTs or observational studies), or several small studies aggregated into a meta-analysis (this is the CancerChoices definition; other researchers and studies may define this differently) of lower blood sugar and insulin resistancea condition in which cells in your muscles, fat, and liver don’t respond well to insulin and can’t efficiently take up glucose from your blood for energy among adults, most of whom are diabetic or prediabetic, treated with probiotics

Good evidence of lower markers of high blood sugar and insulin levels, but no evidence of an effect on peripheral and adipose tissue insulin sensitivity, among adults treated with dietary prebiotics (not specific to cancer)

Hormone imbalance

Changes in hormone levels seen in the studies here may not be beneficial in every situation. Your oncology team needs to determine whether any changes would be favorable for your condition.

Modest evidence of lower levels of ghrelin, a “hunger hormone,” among overweight or obese people treated with prebiotics or synbiotics

No evidence of an effect on leptina hormone that helps regulate energy balance by inhibiting hunger or pancreatic polypeptide levels among prediabetic people treated with prebiotics in a small study

No evidence of an effect on sex hormones during a low-calorie diet among overweight and obese people with hormone-receptor positive (HR+) breast cancer treated with a synbiotic in a small trial

Preliminary evidence of lower testosterone but no evidence of an effect on luteinizing hormone or follicle stimulating hormone among women with polycystic ovarian syndrome treated with synbiotics

Preliminary evidence of a lower marker of stress after elective orthopedic or colorectal surgery among elderly people treated with probiotics

Appetite-related hormones

Modest evidence of lower levels of ghrelin, a “hunger hormone,” among overweight or obese people treated with prebiotics or synbiotics

No evidence of an effect on leptin or pancreatic polypeptide levels among prediabetic people treated with prebiotics in a small study

Lower levels of ghrelin, a “hunger hormone,” among overweight or obese people treated with prebiotics or synbiotics compared to controls in a meta-analysisa statistical analysis that combines the results of two or more research studies; the results of smaller research studies addressing the same or similar questions can be analyzed as though they are one bigger, more powerful study of 4 RCTsrandomized controlled trial, a study design in which people are randomly assigned to either an experimental group or a control group to compare the outcomes from different treatments; an RCT is considered a strong design for determining a therapy’s effects³³da Silva Borges D, Fernandes R et al. Prebiotics may reduce serum concentrations of C-reactive protein and ghrelin in overweight and obese adults: a systematic review and meta-analysis. Nutrition Reviews. 2020 Mar 1;78(3):235-248.
No evidence of an effect on leptin or pancreatic polypeptide levels among prediabetic people treated with xylooligosaccharide prebiotics for 8 weeks compared to placeboa pill, medicine, or procedure—thought to be both harmless and ineffective—prescribed for the psychological benefit to the patient or as a sham treatment in a study to allow a comparison to a therapy of interest in a small RCT³⁴Yang J, Summanen PH et al. Xylooligosaccharide supplementation alters gut bacteria in both healthy and prediabetic adults: a pilot study. Frontiers in Physiology. 2015 Aug 7;6:216.

Sex hormones

No evidence of an effect on sex hormones during a low-calorie diet among overweight and obese people with hormone-receptor positive (HR+) breast cancer treated with a synbiotic in a small trial

Preliminary evidence of lower testosterone but no evidence of an effect on luteinizing hormone or follicle stimulating hormone among women with polycystic ovarian syndrome treated with synbiotics

No evidence of an effect on several sex hormones (estradiol, testosterone, and DHEA-S), or sex hormone binding globulin (SHBG) during a low-calorie diet among overweight and obese people with hormone-receptor positive (HR+) breast cancer treated with a synbiotic supplement compared to placebo in a small RCT³⁵Raji Lahiji M, Najafi S et al. The effect of synbiotic on glycemic profile and sex hormones in overweight and obese breast cancer survivors following a weight-loss diet: a randomized, triple-blind, controlled trial. Clinical Nutrition. 2021 Feb;40(2):394-403.
Lower testosterone but no evidence of an effect on luteinizing hormone or follicle stimulating hormone among women with polycystic ovarian syndrome treated with synbiotics compared to placebo in a small RCT³⁶Esmaeilinezhad Z, Babajafari S et al. Effect of synbiotic pomegranate juice on glycemic, sex hormone profile and anthropometric indices in PCOS: a randomized, triple blind, controlled trial. Nutrition, Metabolism & Cardiovascular Diseases. 2019 Feb;29(2):201-208.

Stress hormones: preliminary evidence of a lower marker of stress after elective orthopedic or colorectal surgery among elderly people treated with probiotics

A lower marker of stress (cortisol) 5 to 7 days after elective orthopedic or colorectal surgery among elderly people treated with probiotics compared to placebo in a mid-sized RCT³⁷Wang P, Yin X et al. Perioperative probiotic treatment decreased the incidence of postoperative cognitive impairment in elderly patients following non-cardiac surgery: a randomised double-blind and placebo-controlled trial. Clinical Nutrition. 2021 Jan;40(1):64-71.

Immune function

Increased immune system activation is not always beneficial, so your oncology team needs to determine whether immune activation would be favorable in your situation.

Preliminary evidence of higher immune activation after surgery among people with liver or colorectal cancer treated with a synbiotic or probiotic

Preliminary evidence of higher immune activation among overweight or obese and insulin-resistant people treated with a probiotic

Preliminary evidence of greater immune responses after liver removal among people with biliary cancer involving the hepatic hilus treated with synbiotics both before and after surgery compared to only after surgery

A higher marker of inflammation (nitric oxide) and one lower indicator of immune activation (IL-6) but no difference in another (TNF-α) among people with depressive symptoms treated with probiotics compared to controls in a meta-analysis of RCTsrandomized controlled trial, a study design in which people are randomly assigned to either an experimental group or a control group to compare the outcomes from different treatments; an RCT is considered a strong design for determining a therapy’s effects³⁸Lin J, Zhang Y et al. The effect and safety of probiotics on depression: a systematic review and meta-analysis of randomized controlled trials. European Journal of Nutrition. 2023 May 29.
A minor stimulatory effect on immune function after curative resection among people with colon cancer treated with a synbiotic comprising Lactobacillus rhamnosus GG, Bifidobacterium lactis Bb12, and inulin enriched with oligofructose compared to placebo in a small RCT³⁹Roller M, Clune Y, Collins K, Rechkemmer G, Watzl B. Consumption of prebiotic inulin enriched with oligofructose in combination with the probiotics Lactobacillus rhamnosus and Bifidobacterium lactis has minor effects on selected immune parameters in polypectomised and colon cancer patients. British Journal of Nutrition. 2007 Apr;97(4):676-84.
Higher markers of immune response (CD3, CD4, CD8, and naive and memory lymphocyte subsets) after elective colorectal resection for cancer among people treated with Bifidobacterium longum and Lactobacillus johnsonii compared to placebo, and a stronger response with a higher dose, in a small RCT⁴⁰Gianotti L, Morelli L et al. A randomized double-blind trial on perioperative administration of probiotics in colorectal cancer patients. World Journal of Gastroenterology. 2010 Jan 14;16(2):167-75.
Some markers of immune activation (no increase in IL-2 among people with polyps, and a weak trend toward higher production of interferon-γ among people with colorectal cancer), but no evidence of an effect on other markers of systemic immune function among people treated with a synbiotic comprising Lactobacillus rhamnosus GG, Bifidobacterium lactis Bb12, and inulin enriched with oligofructose compared to placebo in a small RCT⁴¹Rafter J, Bennett M et al. Dietary synbiotics reduce cancer risk factors in polypectomized and colon cancer patients. American Journal of Clinical Nutrition. 2007 Feb;85(2):488-96.
A higher marker of immune response (IL-6) 72 hours after elective colorectal surgery, but no evidence of an effect on leukocytes count or the lymphocyte/granulocyte ratio among people treated with synbiotics compared to either prebiotics and heat-deactivated probiotics or mechanical bowel cleansing before surgery in a small RCT⁴²Horvat M, Krebs B, Potrc S, Ivanecz A, Kompan L. Preoperative synbiotic bowel conditioning for elective colorectal surgery. Wien Klinishe Wochenschrift. 2010 May;122 Suppl 2:26-30.
Lower immune activity (white blood cell count), which the researchers interpreted as a favorable metabolic change, among overweight or obese and insulin-resistant people treated with pasteurized Akkermansia muciniphila for 3 months compared to placebo in a small RCT⁴³Depommier C, Everard A et al. Supplementation with Akkermansia muciniphila in overweight and obese human volunteers: a proof-of-concept exploratory study. Nature Medicine. 2019 Jul;25(7):1096-1103.
Higher markers of immune function (NK cells and monocytes; plasma levels of immunoglobulins M, A, and G; and IL-10) among healthy adults treated with L. salivarius CECT5713 daily for 4 weeks compared to placebo in a small RCT⁴⁴Sierra S, Lara-Villoslada F et al. Intestinal and immunological effects of daily oral administration of Lactobacillus salivarius CECT5713 to healthy adults. Anaerobe. 2010 Jun;16(3):195-200.
Enhanced immune responses after hepatectomy among people with biliary cancer involving the hepatic hilus treated with synbiotics both before and after surgery compared to only after surgery in a mid-sized RCT⁴⁵Sugawara G, Nagino M et al. Perioperative synbiotic treatment to prevent postoperative infectious complications in biliary cancer surgery: a randomized controlled trial. Annals of Surgery. 2006 Nov;244(5):706-14.

Inflammation

Good evidence of less inflammation after surgery among people with colorectal cancer treated with probiotics or synbiotics

Preliminary evidence of lower markers of inflammation during chemotherapy and radiotherapy among people with cancer treated with a synbiotic

Preliminary evidence of lower markers of inflammation among healthy young volunteers treated with a probiotic, whether with or without prebiotics but stronger effects with prebiotics

Modest evidence of lower markers of inflammation among people with inflammatory conditions, including cancer, treated with probiotics

Strong evidence of one lower marker of inflammation (TNF-α) but not others (C-reactive protein and interleukin-6) among people eating fermented foods: probiotic yogurt (unsweetened and with live cultures), kefir, tempeh, natto, kombucha, miso, kimchi, sauerkraut, or cultured cheese

Insufficient (conflicting) evidence of an effect on inflammation among people with inflammatory conditions treated with prebiotics

Oxidative stress

Insufficient (conflicting) evidence of an effect on oxidative stressan imbalance between free radicals and antioxidants in your body in which antioxidant levels are lower than normal; this imbalance can cause harmful oxidation reactions in your body chemistry among diabetic people treated with probiotics

Your microbiome

Good evidence of a better microbiome status among people with cancer treated with probiotics, including during chemotherapy and surgery

Preliminary evidence of greater gut bacterial diversity and higher levels of the main short-chain fatty acids during chemotherapy after colorectal cancer surgical resection among people treated with probiotic tablets

Preliminary evidence of less disruption to the gut microbiome among people with cancer treated with probiotics

Preliminary evidence of beneficial changes to the fecal microbiome among people with diabetes treated with probiotics

Preliminary evidence of higher abundance of microbial genera after surgery among people treated with probiotics

Preliminary evidence of beneficial changes in the microbiome among healthy people treated with probiotics

Preliminary evidence of less bacterial vaginosis among people treated with oral probiotics

No evidence of an effect on oral bacterial community composition or diversity after radiotherapy among people with head and neck cancer treated with oral probiotics in a small trial

Preliminary evidence of beneficial changes in the microbiomes of people treated with prebiotics

Also see evidence of slower and less complete return to a baseline microbiome after antibiotic treatment among healthy people treated with probiotics in Safety and precautions ›

Probiotics and prebiotics (synbiotics): good evidence of a better microbiome status among people with cancer treated with probiotics, including during chemotherapy and surgery

Less intestinal dysbiosismicrobial imbalance or maladaptation on or inside the body after surgery among people with colorectal cancer treated with probiotics or synbiotics compared to controls in a meta-analysisa statistical analysis that combines the results of two or more research studies; the results of smaller research studies addressing the same or similar questions can be analyzed as though they are one bigger, more powerful study of 19 RCTsrandomized controlled trial, a study design in which people are randomly assigned to either an experimental group or a control group to compare the outcomes from different treatments; an RCT is considered a strong design for determining a therapy’s effects⁶⁵Zeng J, Ji Y et al. The effect of pro/synbiotics on postoperative infections in colorectal cancer patients: a systematic review and meta-analysis. Complementary Therapies in Clinical Practice. 2021 May;43:101370.
Better microenvironment of the gut about 4 to 5 weeks into chemotherapy among children with cancer treated with prebiotics (fructooligosaccharides) and probiotics (Bifidobacterium or Lactobacilli) compared to baseline or controls in a meta-analysis of 7 clinical trials (4 observationala type of study in which individuals are observed or certain outcomes are measured, but no attempt is made to affect the outcome (for example, no treatment is given); an example is a study that records people’s diets, but doesn’t try to alter their diets, and looks for patterns of disease or other outcomes related to different foods and 3 RCTs)⁶⁶Bai J, Behera M, Bruner DW. The gut microbiome, symptoms, and targeted interventions in children with cancer: a systematic review. Supportive Care in Cancer. 2018 Feb;26(2):427-439.
No evidence of an effect on concentrations and total proportions of probiotic and pathogenic bacteria during chemotherapy and radiotherapy among people with cervical cancer treated with a synbiotic of Lactobacillus acidophilus NCFM, Bifidobacterium lactis Bi-07, and blue agave inulin 3 times a day compared to placeboa pill, medicine, or procedure—thought to be both harmless and ineffective—prescribed for the psychological benefit to the patient or as a sham treatment in a study to allow a comparison to a therapy of interest in a small RCT⁶⁷De Loera Rodríguez LH, Ortiz GG et al. Effect of symbiotic supplementation on fecal calprotectin levels and lactic acid bacteria, Bifidobacteria, Escherichia coli and Salmonella DNA in patients with cervical cancer. Nutrición Hospitalaria. 2018 Dec 3;35(6):1394-1400.
More beneficial gut bacteria and fewer harmful gut bacteria during chemotherapy among people with advanced esophageal cancer treated with synbiotics compared to controls in a small RCT⁶⁸Motoori M, Yano M et al. Randomized study of the effect of synbiotics during neoadjuvant chemotherapy on adverse events in esophageal cancer patients. Clinical Nutrition. 2017 Feb;36(1):93-99.
Higher fecal counts of total lactobacilli and lower counts of coliforms and Escherichia coli among healthy young volunteers treated with Lactobacillus salivarus UBL S22, either with or without prebiotics but stronger effects with prebiotics, for 6 weeks compared to placebo in a small RCT⁶⁹Rajkumar H, Kumar M et al. Effect of probiotic Lactobacillus salivarius UBL S22 and prebiotic fructo-oligosaccharide on serum lipids, inflammatory markers, insulin sensitivity, and gut bacteria in healthy young volunteers: a randomized controlled single-blind pilot study. Journal of Cardiovascular Pharmacology and Therapeutics. 2015 May;20(3):289-98.

Probiotics alone

Greater gut bacterial diversity and dramatically higher levels of the main short-chain fatty acids (SCFAs) during a first chemotherapy course after colorectal cancer surgical resection among people treated with tablets combining B. infants, L. acidophilus, E. faecalis, and B. cereus compared to placebo in a mid-sized RCT⁷⁰Huang F, Li S et al. Postoperative probiotics administration attenuates gastrointestinal complications and gut microbiota dysbiosis caused by chemotherapy in colorectal cancer patients. Nutrients. 2023 Jan 11;15(2):356.

Preliminary evidence of beneficial changes in the microbiome among healthy people treated with probiotics

Higher fecal counts of lactobacilli and propionibacteria and lower activity of beta-glucosidase accompanying higher counts of propionibacteria among healthy men treated with Lactobacillus rhamnosus LC705 (LC705) and Propionibacterium freudenreichii ssp shermanii JS (PJS) compared to placebo in a small RCT⁷¹Hatakka K, Holma R et al. The influence of Lactobacillus rhamnosus LC705 together with Propionibacterium freudenreichii ssp. shermanii JS on potentially carcinogenic bacterial activity in human colon. International Journal of Food Microbiology. 2008 Dec 10;128(2):406-10.
Beneficial changes in the microbiome (higher rates of Lactobacillus, lower rates of Clostridium perfringens, lower fecal pH, lower synthesis of fecal putrefaction products, and higher rates of the short-chain fatty acid isobutyric acid) among healthy people treated with Lactobacillus gasseri OLL2716: LG21 for 12 weeks compared to baseline in a small uncontrolled trial⁷²Ohara T, Yoshino K, Kitajima M. Possibility of preventing colorectal carcinogenesis with probiotics. Hepatogastroenterology. 2010 Nov-Dec;57(104):1411-5.

Preliminary evidence of less disruption to the gut microbiome among people with cancer treated with probiotics

Less disruption in microbes, such as a lower increase in Enterobacteriaceae, during chemotherapy among children with cancer treated with the probiotic Bifidobacterium breve strain Yakult compared to placebo in a small RCT⁷³Wada M, Nagata S et al. Effects of the enteral administration of Bifidobacterium breve on patients undergoing chemotherapy for pediatric malignancies. Supportive Care in Cancer. 2010 Jun;18(6):751-9.

Preliminary evidence of beneficial changes to the fecal microbiome among people with diabetes treated with probiotics

Beneficial changes to the microbiome (more butyrate-producing bacteria, especially Faecalibacterium and Clostridiales spp, and less colorectal cancer-associated taxa, Fusobacterium and Peptostreptococcus) among people with colon cancer treated with 2 daily tablets of Bifidobacterium lactis Bl-04 and Lactobacillus acidophilus NCFM compared to controls in a small controlled triala study design in which people are assigned to either an experimental group or a control group to compare the outcomes from different treatment; assignment is not random, and so this is not as strong a study design as a randomized controlled trial, but still stronger than an uncontrolled trial⁷⁴Hibberd AA, Lyra A et al. Intestinal microbiota is altered in patients with colon cancer and modified by probiotic intervention. BMJ Open Gastroenterology. 2017 Jul 3;4(1):e000145.
Higher levels of Lactobacillus reuteri and other changes in fecal microbes among people with type 2 diabetes after being treated with L. reuteri for 3 months compared to controls in a small RCT:⁷⁵Hsieh MC, Tsai WH et al. The beneficial effects of Lactobacillus reuteri ADR-1 or ADR-3 consumption on type 2 diabetes mellitus: a randomized, double-blinded, placebo-controlled trial. Scientific Reports. 2018 Nov 14;8(1):16791.
- Increase in Bifidobacterium spp. and Lactobacillus spp. among people treated with either ADR-1 or ADR-3 strains of Lactobacillus reuteri
- Decrease in Bacteroidetes among people treated with L. reuteri strain ADR-1
- Increase in Firmicutes among people treated with L. reuteri strain ADR-3

Preliminary evidence of higher abundance of microbial genera after surgery among people treated with probiotics

More change in the relative abundance of microbial genera after elective orthopedic or colorectal surgery among elderly people treated with probiotics compared to placebo in a mid-sized RCT⁷⁶Wang P, Yin X et al. Perioperative probiotic treatment decreased the incidence of postoperative cognitive impairment in elderly patients following non-cardiac surgery: a randomised double-blind and placebo-controlled trial. Clinical Nutrition. 2021 Jan;40(1):64-71.

Preliminary evidence of less bacterial vaginosis among people treated with oral probiotics

Less bacterial vaginosis (Nugent scores) among people with bacterial vaginosis and treated with of 4 Lactobacillus strains orally compared to placebo in a meta-analysis of 3 RCTs⁷⁷de Vrese M, Laue C, Papazova E, Petricevic L, Schrezenmeir J. Impact of oral administration of four Lactobacillus strains on Nugent score —systematic review and meta-analysis. Beneficial Microbes. 2019 May 28;10(5):483-496.

No evidence of an effect on oral bacterial community composition or diversity after radiotherapy among people with head and neck cancer treated with oral probiotics in a small trial

No evidence of an effect on oral bacterial community composition or diversity after radiotherapy among people with head and neck cancer treated with oral probiotic lozenges containing Streptococcus salivarius M18 for 4 weeks compared to placebo in a small controlled trial⁷⁸Vesty A, Gear K et al. Randomised, double-blind, placebo-controlled trial of oral probiotic Streptococcus salivarius M18 on head and neck cancer patients post-radiotherapy: a pilot study. Scientific Reports. 2020 Aug 6;10(1):13201.

Prebiotics alone: preliminary evidence of beneficial changes in the microbiomes of people treated with prebiotics

Higher Bifidobacteria counts among people with cancer treated with 10 g partially hydrolyzed guar gum twice a day 14 days prior and 14 days during pelvic radiation compared to placebo in a small RCT⁷⁹Rosli D, Shahar S et al. Randomized controlled trial on the effect of partially hydrolyzed guar gum supplementation on diarrhea frequency and gut microbiome count among pelvic radiation patients. JPEN Journal of Parenteral and Enteral Nutrition. 2021 Feb;45(2):277-286.
5-fold increase in abundance of fecal Bifidobacterium species but no evidence of an effect on short-chain fatty acid concentrations among overweight or obese (body mass index 28-40), prediabetic men and women treated with galacto-oligosaccharides for 12 weeks compared to placebo (maltodextrin) in a small RCT⁸⁰Canfora EE, van der Beek CM et al. Supplementation of diet with galacto-oligosaccharides increases bifidobacteria, but not insulin sensitivity, in obese prediabetic individuals. Gastroenterology. 2017 Jul;153(1):87-97.e3.
Changes in fecal microbial abundance among healthy or prediabetic people treated with xylooligosaccharide prebiotics for 8 weeks compared to placebo in a small RCT⁸¹Yang J, Summanen PH et al. Xylooligosaccharide supplementation alters gut bacteria in both healthy and prediabetic adults: a pilot study. Frontiers in Physiology. 2015 Aug 7;6:216.
- Decreases in abundance of Howardella, Enterorhabdus, and Slackia among either healthy or prediabetic people
- An increase in Blautia hydrogenotrophica among prediabetic people
No decline in the number of fecal Bifidobacteria among home-living adults receiving tube feedings enriched with fructo-oligosaccharides and fiber compared to declines among people receiving no-residue tube feeding in a small controlled trial⁸²Wierdsma NJ, van Bodegraven AA et al. Fructo-oligosaccharides and fibre in enteral nutrition has a beneficial influence on microbiota and gastrointestinal quality of life. Scandinavian Journal of Gastroenterology. 2009;44(7):804-12.

See Your Microbiome › for more information about its role in cancer.

Other terrain factors

Preliminary evidence of better intestinal pH during chemotherapy among children treated with a probiotic

Weak evidence of less intestinal absorption of aflatoxin B1 , which is associated with an increased risk of liver cancer

No evidence of an effect on trimethylamine N-oxide (TMAO)—a promoter of atherosclerosis and linked to colorectal cancer—among people with metabolic syndrome treated with Lactobacillus casei Shirota

Preliminary evidence of better intestinal pH during chemotherapy among children treated with a probiotic

Maintained intestinal pH below 7.0 during chemotherapy among children treated with the probiotic Bifidobacterium breve strain Yakult compared to rises in pH with placeboa pill, medicine, or procedure—thought to be both harmless and ineffective—prescribed for the psychological benefit to the patient or as a sham treatment in a study to allow a comparison to a therapy of interest in a small RCTrandomized controlled trial, a study design in which people are randomly assigned to either an experimental group or a control group to compare the outcomes from different treatments; an RCT is considered a strong design for determining a therapy’s effects⁸³Wada M, Nagata S et al. Effects of the enteral administration of Bifidobacterium breve on patients undergoing chemotherapy for pediatric malignancies. Supportive Care in Cancer. 2010 Jun;18(6):751-9.

Weak evidence of less intestinal absorption of aflatoxin B1 , which is associated with an increased risk of liver cancer

A weak trend toward more samples testing negative for AFB-N7-guanine—indicating less intestinal absorption of aflatoxin B1, which is associated with an increased risk of liver cancer—among healthy young men treated with Lactobacillus rhamnosus LC705 and Propionibacterium freudenreichii subsp. shermanii strains 2 times a day for 5 weeks compared to placebo in a small RCT⁸⁴El-Nezami HS, Polychronaki NN et al. Probiotic supplementation reduces a biomarker for increased risk of liver cancer in young men from Southern China. American Journal of Clinical Nutrition. 2006 May;83(5):1199-203.

No evidence of an effect on trimethylamine N-oxide (TMAO) › among people with metabolic syndrome treated with Lactobacillus casei Shirota for 12 weeks compared to standard therapy in a small RCT⁸⁵Tripolt NJ, Leber B et al. Effect of Lactobacillus casei Shirota supplementation on trimethylamine-N-oxide levels in patients with metabolic syndrome: an open-label, randomized study. Atherosclerosis. 2015 Sep;242(1):141-4.

Probiotics combined with other therapies

Preliminary evidence of comparable rates of infections and duration of neutropenic episodes, with fewer side effects among children with leukemia and solid tumors treated with a preparation of co-trimoxazole and Lactobacilli compared to framycetin, colymycin, nystatin, and metronidazole

Preliminary evidence of lower rates of infectious complication, a higher marker of immune activation (NK cells), lower marker of infection (PCT), and lower fasting insulin and insulin resistance index after surgery among people with upper gastrointestinal perforation/abdominal infection treated with probiotics, deep sea fish oil, glutamine and a commercial nutrition supplement (Nutrison)

Preliminary evidence of higher levels of brain-derived neurotrophic factor but no evidence of an effect on a marker of inflammation among people with depression and chronic diarrhea treated with electroacupuncture combined with a probiotic

Probiotic preparation and co-trimoxazole: preliminary evidence of comparable rates of infections and duration of neutropenic episodes, with fewer side effects among children with leukemia and solid tumors treated with a preparation of co-trimoxazole and Lactobacilli compared to framycetin, colymycin, nystatin, and metronidazole

Comparable rates of infections and duration of neutropenic episodes among children with leukemia and solid tumors treated with a preparation of co-trimoxazole and Lactobacilli compared to framycetin, colymycin, nystatin, and metronidazole; the co-trimoxazole and lactobacilli preparation was also better tolerated (no nausea and vomiting, no refusal to take medication, no dose reduction or change to an alternative regimen) in a small controlled studya study design in which people are assigned to either an experimental group or a control group to compare the outcomes from different treatment; assignment is not random, and so this is not as strong a study design as a randomized controlled trial, but still stronger than an uncontrolled trial⁸⁶Ekert H, Jurk IH, Waters KD, Tiedemann K. Prophylactic co-trimoxazole and lactobacilli preparation in neutropenic patients. Medical and Pediatric Oncology. 1980;8(1):47-51.

Probiotics, deep sea fish oil, glutamine and a commercial nutrition supplement: preliminary evidence of lower rates of infectious complication, a higher marker of immune function (NK cells), lower marker of infection (PCT), and lower fasting insulin and insulin resistance index after surgery among people with upper gastrointestinal perforation/abdominal infection treated with probiotics, deep sea fish oil, glutamine and a commercial nutrition supplement (Nutrison)

Lower rates of infectious complication, a higher marker of immune function (NK cells), lower marker of infection (PCT), and lower fasting insulin and insulin resistance index after surgery among people with upper gastrointestinal perforation/abdominal infection treated with probiotics, deep sea fish oil, glutamine, and a commercial nutrition supplement (Nutrison) compared to conventional enteral nutrition in a small RCTrandomized controlled trial, a study design in which people are randomly assigned to either an experimental group or a control group to compare the outcomes from different treatments; an RCT is considered a strong design for determining a therapy’s effects⁸⁷Shao F, Yang D. [Impact of microbial immune enteral nutrition on postoperative insulin resistance and infectious complication of patients with abdominal infection][Article in Chinese]. Zhonghua Wei Chang Wai Ke Za Zhi. 2014 Jul;17(7):676-9.

Probiotics and electroacupuncture: preliminary evidence of higher levels of brain-derived neurotrophic factor but no evidence of an effect on a marker of inflammation among people with depression and chronic diarrhea treated with electroacupuncture combined with a probiotic

Higher levels of brain-derived neurotrophic factor—which influences or regulates neuronal survival and growth and also glucose and energy metabolism—but no evidence of an effect on a marker of inflammation (serum inflammatory cytokines) among people with depression and chronic diarrhea treated with electroacupuncture combined with viable bifidobacterium quadruple tablets (1.5 g per time, 3 times a day) with warm water after meals compared to conventional drugs for depression and chronic diarrhea in a mid-sized RCT⁸⁸Huang W, Gan W et al. Efficacy of electroacupuncture combined with probiotics for depression and chronic diarrhea in patients and effect on serum inflammatory cytokines, NE and BDNF. Experimental and Therapeutic Medicine. 2019 Nov;18(5):3470-3474.

Managing side effects and promoting wellness

Are probiotics and prebiotics linked to fewer or less severe side effects or symptoms? Are they linked to less toxicity from cancer treatment? Do they support your quality of life or promote general well-being? We present the evidence.

Depression

Preliminary evidencesignificant effects in small or poorly designed clinical studies OR conflicting results in adequate studies but a preponderance of evidence of an effect (this is the CancerChoices definition; other researchers and studies may define this differently) of lower depression scores after completing cancer treatment among people with colorectal cancer treated with probiotics

Fatigue

Preliminary evidence of lower fatigue scores after completing cancer treatment among people with colorectal cancer treated with probiotics

Gastrointestinal symptoms

Preliminary evidence of fewer chemotherapy-induced gastrointestinal complications during chemotherapy after colorectal cancer surgical resection among people treated with probiotic tablets

Good evidence of better bowel function after cancer treatment, including surgery, among people treated with probiotics

Preliminary evidence of less functional constipation during chemotherapy among people with cancer treated with a probiotic

Good evidence of lower risk and severity of treatment-induced diarrhea among people with cancer treated with probiotics, although some variations are seen across populations and treatments

Preliminary evidence of lower frequency of diarrhea during pelvic radiation among people treated with a prebiotic

Preliminary evidence of lower frequency and intensity of vomiting but no evidence of an effectoverall, one or more studies did not demonstrate that a treatment or intervention led to an expected outcome; this does not always mean that there is no effect in clinical practice, but that the studies may have been underpowered (too few participants) or poorly designed. Larger, well-designed studies provide more confidence in making assessments. on nausea during chemotherapy and radiotherapy among people with cervical cancer treated with a synbiotic

Oral symptoms

Good evidence of lower incidence and severity of oral mucositisinflammation and ulceration of the mucous membranes lining the digestive tract, usually as an adverse effect of chemotherapy and radiotherapy treatment for cancer during cancer treatment among people with cancer treated with probiotics

Preliminary evidence of less oral infection after completing head and neck radiotherapy among people with cancer treated with probiotic sachets

No evidence of an effect on periodontal screening and plaque index scores after radiotherapy among people with head and neck cancer treated with oral probiotic lozenges in a small trial

Mucositis: good evidence of lower incidence and severity of oral mucositis during cancer treatment among people with cancer treated with probiotics

Lower incidence of cancer therapy–induced oral mucositis and lower need for enteral nutrition among people treated with probiotics compared to controls in a meta-analysisa statistical analysis that combines the results of two or more research studies; the results of smaller research studies addressing the same or similar questions can be analyzed as though they are one bigger, more powerful study of 7 RCTsrandomized controlled trial, a study design in which people are randomly assigned to either an experimental group or a control group to compare the outcomes from different treatments; an RCT is considered a strong design for determining a therapy’s effects¹⁰⁹Liu YC, Wu CR, Huang TW. Preventive effect of probiotics on oral mucositis induced by cancer treatment: a systematic review and meta-analysis. International Journal of Molecular Sciences. 2022 Oct 31;23(21):13268.
Lower incidence and severity of chemotherapy-induced oral mucositis, mostly among Asian people, treated with oral probiotics compared to controls, and stronger effects with use of more probiotic species in a meta-analysis of 4 RCTs¹¹⁰Feng J, Gao M et al. Oral administration of probiotics reduces chemotherapy-induced diarrhea and oral mucositis: a systematic review and meta-analysis. Frontiers in Nutrition. 2022 Feb 28;9:823288.
A lower incidence and severity of oral mucositis during cancer treatment among people with cancer treated with probiotics compared to placeboa pill, medicine, or procedure—thought to be both harmless and ineffective—prescribed for the psychological benefit to the patient or as a sham treatment in a study to allow a comparison to a therapy of interest in a meta-analysis of 4 RCTs¹¹¹Shu Z, Li P, Yu B, Huang S, Chen Y. The effectiveness of probiotics in prevention and treatment of cancer therapy-induced oral mucositis: a systematic review and meta-analysis. Oral Oncology. 2020 Mar;102:104559.

Oral infection: preliminary evidence of less oral infection after completing head and neck radiotherapy among people with cancer treated with probiotic sachets

Less oral infection (lower counts of Candida species) after completing head and neck radiotherapy among people with cancer treated with Darolac® probiotic sachets containing probiotic strains Lactobacillus acidophilus, Lactobacillus rhamnosus, Bifidobacterium longum, and Saccharomyces boulardii, either alone or with the antifungal agent clotrimazole 1% (candid mouth paint) compared to clotrimazole alone in a small RCT¹¹²Doppalapudi R, Vundavalli S, Prabhat MP. Effect of probiotic bacteria on oral Candida in head- and neck-radiotherapy patients: a randomized clinical trial. Journal of Cancer Research and Therapeutics. 2020 Apr-Jun;16(3):470-477.

Periodontal screening and plaque: no evidence of an effect on periodontal screening and plaque index scores after radiotherapy among people with head and neck cancer treated with oral probiotic lozenges in a small trial

No evidence of an effect on periodontal screening and plaque index scores after radiotherapy among people with head and neck cancer treated with oral probiotic lozenges containing Streptococcus salivarius M18 for 4 weeks compared to placebo in a small controlled triala study design in which people are assigned to either an experimental group or a control group to compare the outcomes from different treatment; assignment is not random, and so this is not as strong a study design as a randomized controlled trial, but still stronger than an uncontrolled trial¹¹³Vesty A, Gear K et al. Randomised, double-blind, placebo-controlled trial of oral probiotic Streptococcus salivarius M18 on head and neck cancer patients post-radiotherapy: a pilot study. Scientific Reports. 2020 Aug 6;10(1):13201.

Quality of life

Preliminary evidence of better quality of life scores among people with colorectal cancer treated with probiotics

Stress

Preliminary evidence of less stress (no elevation in markers of stress) among people with laryngeal cancer awaiting laryngectomy treated with probiotics

Recovery after surgery

Good evidence of less infection, shorter hospital stays, and other indicators of better recovery after surgery among people with gastrointestinal cancer, including colorectal cancer, treated with probiotics or synbiotics

Preliminary evidence of fewer infectious complications after liver removal among people with biliary cancer treated with synbiotics both before and after surgery compared to only after surgery

Good evidence of lower risk of infection after colorectal cancer surgery among people treated with probiotics

Preliminary evidence of fewer infectious complications after Whipple procedure among people treated with probiotics

Probiotics or synbiotics

Preliminary evidence of fewer bacterial infections and fewer days of antibiotic treatment, plus a weak trend toward shorter hospital stays, after Whipple procedure among people treated with probiotics

Shorter time to first fluid diet and first solid diet, shorter hospital stays, and lower incidence of postoperative ileus after surgery among people with gastrointestinal cancer treated with probiotics or synbiotics compared to controls in a meta-analysisa statistical analysis that combines the results of two or more research studies; the results of smaller research studies addressing the same or similar questions can be analyzed as though they are one bigger, more powerful study of 21 RCTsrandomized controlled trial, a study design in which people are randomly assigned to either an experimental group or a control group to compare the outcomes from different treatments; an RCT is considered a strong design for determining a therapy’s effects¹¹⁶Tang G, Huang W, Tao J, Wei Z. Prophylactic effects of probiotics or synbiotics on postoperative ileus after gastrointestinal cancer surgery: a meta-analysis of randomized controlled trials. PLoS One. 2022 Mar 1;17(3):e0264759.
Fewer infections, including both surgical and nonsurgical site infections, and non-infectious complications after surgery among people with colorectal cancer treated with probiotics or synbiotics compared to controls in a meta-analysis of 19 RCTs¹¹⁷Zeng J, Ji Y et al. The effect of pro/synbiotics on postoperative infections in colorectal cancer patients: a systematic review and meta-analysis. Complementary Therapies in Clinical Practice. 2021 May;43:101370.
Fewer surgical site infections after elective surgery among people with colorectal cancer treated with synbiotics for 5 days prior to and for 14 days after surgery compared to placeboa pill, medicine, or procedure—thought to be both harmless and ineffective—prescribed for the psychological benefit to the patient or as a sham treatment in a study to allow a comparison to a therapy of interest in a small RCT¹¹⁸Flesch AT, Tonial ST, Contu PC, Damin DC. Perioperative synbiotics administration decreases postoperative infections in patients with colorectal cancer: a randomized, double-blind clinical trial. Revista do Colegio Brasileiro de Cirurgioes. 2017 Nov-Dec;44(6):567-573. English, Portuguese.
Fewer bacterial infections and fewer days of antibiotic treatment, plus a weak trend toward shorter hospital stays, after pylorus-preserving Whipple procedure (pancreatoduodenectomy) among people treated with enteral nutrition enriched with 4 different lactic acid bacteria and 4 fibers starting the day before surgery and continuing for 8 days compared to the 4 fibers without Lactobacillus in a small RCT¹¹⁹Rayes N, Seehofer D et al. Effect of enteral nutrition and synbiotics on bacterial infection rates after pylorus-preserving pancreatoduodenectomy: a randomized, double-blind trial. Annals of Surgery. 2007 Jul;246(1):36-41.

Synbiotics before and after surgery compared to only after surgery: preliminary evidence of fewer infectious complications after liver removal among people with biliary cancer treated with synbiotics both before and after surgery

Fewer infectious complications after liver removal among people with biliary cancer involving the hepatic hilus treated with synbiotics both before and after surgery compared to only after surgery in a mid-sized RCT¹²⁰Sugawara G, Nagino M et al. Perioperative synbiotic treatment to prevent postoperative infectious complications in biliary cancer surgery: a randomized controlled trial. Annals of Surgery. 2006 Nov;244(5):706-14.

Probiotics alone

Good evidence of lower risk of infection after colorectal cancer surgery among people treated with probiotics

Preliminary evidence of fewer infectious complications after pancreaticoduodenectomy among people treated with probiotics

66% lower risk of infection after colorectal cancer surgery among people treated with probiotics before and after surgery compared to placebo in a meta-analysis of 16 RCTs¹²¹Amitay EL, Carr PR, Gies A, Laetsch DC, Brenner H. Probiotic/synbiotic treatment and postoperative complications in colorectal cancer patients: systematic review and meta-analysis of randomized controlled trials. Clinical and Translational Gastroenterology. 2020 Dec;11(12):e00268.
49% lower risk of overall infection after colorectal cancer surgery among people treated with probiotics before and after surgery in a meta-analysis of 12 RCTs and 1 controlled triala study design in which people are assigned to either an experimental group or a control group to compare the outcomes from different treatment; assignment is not random, and so this is not as strong a study design as a randomized controlled trial, but still stronger than an uncontrolled trial¹²²Ouyang X, Li Q et al. Probiotics for preventing postoperative infection in colorectal cancer patients: a systematic review and meta-analysis. International Journal of Colorectal Disease. 2019 Mar;34(3):459-469.
Fewer surgical site infections, infectious complications, and pathogens in the blood after colorectal cancer surgery among people treated with probiotics before and after surgery compared to controls in a meta-analysis of 7 RCTs¹²³de Andrade Calaça PR, Bezerra RP, Albuquerque WWC, Porto ALF, Cavalcanti MTH. Probiotics as a preventive strategy for surgical infection in colorectal cancer patients: a systematic review and meta-analysis of randomized trials. Translational Gastroenterology and Hepatology. 2017 Aug 23;2:67.
Fewer infectious complications after Whipple procedure (pancreaticoduodenectomy) among people treated with probiotics immediately after admission—3 to 15 days before surgery—and then reintroduced on the second day after surgery and until hospital discharge compared to controls in a small RCT¹²⁴Nomura T, Tsuchiya Y et al. Probiotics reduce infectious complications after pancreaticoduodenectomy. Hepatogastroenterology. 2007 Apr-May;54(75):661-3.
Lower intestinal permeability and levels of zonulin (a regulator of intestinal permeability) after colectomy for colorectal cancer among people treated with probiotics for 6 days before surgery and 10 days after surgery compared to placebo in a mid-sized RCT¹²⁵Liu ZH, Huang MJ et al. The effects of perioperative probiotic treatment on serum zonulin concentration and subsequent postoperative infectious complications after colorectal cancer surgery: a double-center and double-blind randomized clinical trial. American Journal of Clinical Nutrition. 2013 Jan;97(1):117-26.

Symptoms not specific to cancer

Insufficient (conflicting) evidencepreclinical evidence only OR clinical studies with such poor or unclear methodology that no conclusion can be drawn OR conflicting findings across clinical studies with no preponderance of evidence in one direction; conflicting evidence occurs when studies find conflicting effects (positive effect vs no effect or negative effect) with the same treatment and the same general study population (same cancer type, for example) (this is the CancerChoices definition; other researchers and studies may define this differently) of an effect on anxiety among people treated with probiotics (not specific to cancer)

Good evidence of higher self-reported feelings of satiety among healthy adults treated with dietary prebiotics (not specific to cancer)

Preliminary evidence of less cognitive impairment after elective orthopedic or colorectal surgery among elderly people treated with probiotics (not specific to cancer)

Good evidence of less depression among people with symptoms of depression treated with probiotics (not specific to cancer)

Good evidence of shorter duration of diarrhea during antibiotic therapy among patients treated with specific probiotics (not specific to cancer)

Modest evidencesignificant effects in at least three small but well-designed randomized controlled trials (RCTs), or one or more well-designed, mid-sized clinical studies of reasonably good quality (RCTs or observational studies), or several small studies aggregated into a meta-analysis (this is the CancerChoices definition; other researchers and studies may define this differently) of less constipation among people treated with probiotics (not specific to cancer)

No evidence of an effect on gastrointestinal function after elective orthopedic or colorectal surgery (not specific to cancer) among elderly people treated with probiotics in a small trial

Preliminary evidence of lower markers of enzymes indicating liver dysfunction among overweight or obese and insulin-resistant people treated with a probiotic (not specific to cancer)

No evidence of an effect on pain intensity after elective orthopedic or colorectal surgery among elderly people treated with probiotics in a small trial (not specific to cancer)

Preliminary evidence of maintained quality of life scores among home-living adults receiving tube feedings enriched with prebiotics (not specific to cancer)

No evidence of an effect on sleep quality after elective orthopedic or colorectal surgery among elderly people treated with probiotics in a small trial (not specific to cancer)

No evidence of an effect on stress among people with symptoms of stress treated with probiotics in a combined analysis of studies (not specific to cancer)

Modest evidence of less perceived stress among healthy volunteers treated with probiotics (not specific to cancer)

Preliminary evidence of a lower marker of stress 5 to 7 days after elective orthopedic or colorectal surgery among elderly people treated with probiotics (not specific to cancer)

Good evidence of less surgical site infection, pneumonia, or sepsis, plus shorter duration of antibiotic administration and hospital stays after surgery (not specific to cancer) among people treated with synbiotic therapy

Preliminary evidence of lower incidence of multiorgan failure, septic complications, and mortality among people with severe acute pancreatitis treated with synbiotics (not specific to cancer)

Anxiety: insufficient (conflicting) evidence of an effect on anxiety among people treated with probiotics

Slightly less anxiety among people with anxiety symptoms treated with probiotics compared to controls in a meta-analysisa statistical analysis that combines the results of two or more research studies; the results of smaller research studies addressing the same or similar questions can be analyzed as though they are one bigger, more powerful study of 34 controlled trialsa study design in which people are assigned to either an experimental group or a control group to compare the outcomes from different treatment; assignment is not random, and so this is not as strong a study design as a randomized controlled trial, but still stronger than an uncontrolled trial¹²⁶Liu RT, Walsh RFL, Sheehan AE. Prebiotics and probiotics for depression and anxiety: a systematic review and meta-analysis of controlled clinical trials. Neuroscience and Biobehavioral Reviews. 2019 Jul;102:13-23.
No effect on anxiety among people with symptoms of anxiety treated with probiotics compared to placeboa pill, medicine, or procedure—thought to be both harmless and ineffective—prescribed for the psychological benefit to the patient or as a sham treatment in a study to allow a comparison to a therapy of interest in a meta-analysis of 23 controlled trials¹²⁷Zagórska A, Marcinkowska M, Jamrozik M, Wiśniowska B, Paśko P. From probiotics to psychobiotics—the gut-brain axis in psychiatric disorders. Beneficial Microbes. 2020 Dec 2;11(8):717-732.
Fewer symptoms of preclinical anxiety among healthy volunteers treated with probiotics compared to placebo in a meta-analysis of 7 RCTsrandomized controlled trial, a study design in which people are randomly assigned to either an experimental group or a control group to compare the outcomes from different treatments; an RCT is considered a strong design for determining a therapy’s effects¹²⁸McKean J, Naug H, Nikbakht E, Amiet B, Colson N. Probiotics and subclinical psychological symptoms in healthy participants: a systematic review and meta-analysis. Journal of Alternative and Complementary Medicine. 2017 Apr;23(4):249-258.
Greater improvements in anxiety symptoms among adults with major depressive disorder treated with multistrain probiotics compared to placebo in a small RCT¹²⁹Nikolova VL, Cleare AJ, Young AH, Stone JM. Acceptability, tolerability, and estimates of putative treatment effects of probiotics as adjunctive treatment in patients with depression: a randomized clinical trial. JAMA Psychiatry. 2023 Jun 14:e231817.

Changes in appetite: good evidence of higher self-reported feelings of satiety among healthy adults treated with dietary prebiotics

Higher self-reported feelings of satiety among healthy adults treated with dietary prebiotics compared to controls in a meta-analysis of 26 RCTs¹³⁰Kellow NJ, Coughlan MT, Reid CM. Metabolic benefits of dietary prebiotics in human subjects: a systematic review of randomised controlled trials. British Journal of Nutrition. 2014 Apr 14;111(7):1147-61.

Cognitive difficulties: preliminary evidence of less cognitive impairment after elective orthopedic or colorectal surgery among elderly people treated with probiotics

Less cognitive impairment after elective orthopedic or colorectal surgery among elderly people treated with probiotics compared to placebo in a mid-sized RCT¹³¹Wang P, Yin X et al. Perioperative probiotic treatment decreased the incidence of postoperative cognitive impairment in elderly patients following non-cardiac surgery: a randomised double-blind and placebo-controlled trial. Clinical Nutrition. 2021 Jan;40(1):64-71.

Depression or mood: good evidence of less depression among people with symptoms of depression treated with probiotics

Lower depression scale scores among people with depressive symptoms treated with probiotics compared to controls in a meta-ananlysis of RCTs¹³²Lin J, Zhang Y et al. The effect and safety of probiotics on depression: a systematic review and meta-analysis of randomized controlled trials. European Journal of Nutrition. 2023 May 29.
Less depression among people with symptoms of depression treated with probiotics compared to placebo in a meta-analysis of 23 controlled trials¹³³Zagórska A, Marcinkowska M, Jamrozik M, Wiśniowska B, Paśko P. From probiotics to psychobiotics—the gut-brain axis in psychiatric disorders. Beneficial Microbes. 2020 Dec 2;11(8):717-732.
Fewer depressive symptoms among people with major depressive disorder treated with probiotics compared to controls in a meta-analysis of 6 controlled trials¹³⁴Sanada K, Nakajima S et al. Gut microbiota and major depressive disorder: a systematic review and meta-analysis. Journal of Affective Disorders. 2020 Apr 1;266:1-13.
Less depression among people with depressive symptoms, with greater effects among people in psychiatric studies, when treated with probiotics compared to controls in a meta-analysis of 34 controlled trials¹³⁵Liu RT, Walsh RFL, Sheehan AE. Prebiotics and probiotics for depression and anxiety: a systematic review and meta-analysis of controlled clinical trials. Neuroscience and Biobehavioral Reviews. 2019 Jul;102:13-23.
Fewer depressive symptoms among people with major depressive disorder treated with probiotics compared to controls, but not among people with other clinical conditions or the general population, in a meta-analysis of 19 RCTs¹³⁶Go KK, Liu YW et al. Effect of probiotics on depressive symptoms: a meta-analysis of human studies. Psychiatry Research. 2019 Dec;282:112568.
Better mood among people with mild to moderate symptoms of depression when treated with probiotics compared to controls in a meta-analysis of 10 RCTs¹³⁷Ng QX, Peters C, Ho CYX, Lim DY, Yeo WS. A meta-analysis of the use of probiotics to alleviate depressive symptoms. Journal of Affective Disorders. 2018 Mar 1;228:13-19.
Fewer symptoms of preclinical depression among healthy volunteers treated with probiotics compared to placebo in a meta-analysis of 7 RCTs¹³⁸McKean J, Naug H, Nikbakht E, Amiet B, Colson N. Probiotics and subclinical psychological symptoms in healthy participants: a systematic review and meta-analysis. Journal of Alternative and Complementary Medicine. 2017 Apr;23(4):249-258.
Lower depression scale scores among people either with or without major depressive disorder treated with probiotics compared to controls, with benefits among people younger than 60 but not older than 65, in a meta-analysis of 5 RCTs of moderate to high quality¹³⁹Huang R, Wang K, Hu J. Effect of probiotics on depression: a systematic review and meta-analysis of randomized controlled trials. Nutrients. 2016 Aug 6;8(8):483.
Greater improvements in depressive symptoms among adults with major depressive disorder treated with multistrain probiotics compared to placebo in a small RCT¹⁴⁰Nikolova VL, Cleare AJ, Young AH, Stone JM. Acceptability, tolerability, and estimates of putative treatment effects of probiotics as adjunctive treatment in patients with depression: a randomized clinical trial. JAMA Psychiatry. 2023 Jun 14:e231817.

Gastrointestinal symptoms

Good evidence of shorter duration of diarrhea during antibiotic therapy among people treated with specific probiotics (not specific to cancer)

Modest evidence of less constipation among people treated with probiotics (not specific to cancer)

No evidence of an effect on gastrointestinal function after elective orthopedic or colorectal surgery (not specific to cancer)among elderly people treated with probiotics in a small trial

Preliminary evidence of fewer stress-induced gastrointestinal symptoms among people with symptoms of stress treated with a probiotic (not specific to cancer)

Preliminary evidence of improved frequency of defecation among healthy adults treated with a probiotic

Preliminary evidence of lower markers of enzymes indicating liver dysfunction among overweight or obese and insulin-resistant people treated with a probiotic (not specific to cancer)

Shorter duration of diarrhea during antibiotic therapy among people treated with specific probiotics in a systematic review and Delphi consensusalso called Delphi technique or Delphi study, this approach assesses consensus among experts through a series of rounds in which each person provides anonymous input on a question; participants are able to see responses from previous rounds of 13 studies¹⁴¹Hungin APS, Mitchell CR et al; European Society for Primary Care Gastroenterology. Systematic review: probiotics in the management of lower gastrointestinal symptoms—an updated evidence-based international consensus. Alimentary Pharmacology and Therapeutics. 2018 Apr;47(8):1054-1070.
Fewer symptoms of constipation among constipated adult women treated with a synbiotic combining fructooligosaccharides with Lactobacillus and Bifidobacterium strains for 30 days compared to placebo (maltodextrin) in a mid-sized RCT¹⁴²Waitzberg DL, Logullo LC et al. Effect of synbiotic in constipated adult women—a randomized, double-blind, placebo-controlled study of clinical response. Clinical Nutrition. 2013 Feb;32(1):27-33.
Fewer symptoms of constipation among people with Parkinson’s disease and constipation treated with Lactobacillus casei Shirota for 5 weeks compared to baseline in a small uncontrolled triala study in which a therapy is used, but without a comparison group against which to judge outcomes; an uncontrolled trial is considered a weak study design¹⁴³Cassani E, Privitera G et al. Use of probiotics for the treatment of constipation in Parkinson’s disease patients. Minerva Gastroenterologica e Dietologica. 2011 Jun;57(2):117-21.
Fewer symptoms of constipation among children with functional chronic intestinal constipation treated with yogurt supplemented with Bifidobacterium longum for 5 weeks compared to plain yogurt in a small RCT¹⁴⁴Guerra PV, Lima LN et al. Pediatric functional constipation treatment with Bifidobacterium-containing yogurt: a crossover, double-blind, controlled trial. World Journal of Gastroenterology. 2011 Sep 14;17(34):3916-21.
No evidence of an effect on gastrointestinal function after elective orthopedic or colorectal surgery among elderly people treated with probiotics compared to placebo in a mid-sized RCT¹⁴⁵Wang P, Yin X et al. Perioperative probiotic treatment decreased the incidence of postoperative cognitive impairment in elderly patients following non-cardiac surgery: a randomised double-blind and placebo-controlled trial. Clinical Nutrition. 2021 Jan;40(1):64-71.
Fewer stress-induced gastrointestinal symptoms (abdominal pain and nausea/vomiting) among people with symptoms of stress treated with a probiotic containing Lactobacillus acidophilus Rosell-52 and Bifidobacterium longum Rosell-175 for 3 weeks compared to placebo in a small RCT¹⁴⁶Diop L, Guillou S, Durand H. Probiotic food supplement reduces stress-induced gastrointestinal symptoms in volunteers: a double-blind, placebo-controlled, randomized trial. Nutrition Research. 2008 Jan;28(1):1-5.
Improved frequency of defecation among healthy adults treated with L. salivarius CECT5713 daily for 4 weeks compared to placebo in a small RCT¹⁴⁷Sierra S, Lara-Villoslada F et al. Intestinal and immunological effects of daily oral administration of Lactobacillus salivarius CECT5713 to healthy adults. Anaerobe. 2010 Jun;16(3):195-200.
Lower markers of enzymes indicating liver dysfunction among overweight or obese and insulin-resistant people treated with Akkermansia muciniphila for 3 months compared to placebo in a small RCT¹⁴⁸Depommier C, Everard A et al. Supplementation with Akkermansia muciniphila in overweight and obese human volunteers: a proof-of-concept exploratory study. Nature Medicine. 2019 Jul;25(7):1096-1103.

Pain: no evidence of an effect on pain intensity after elective orthopedic or colorectal surgery among elderly people treated with probiotics in a small trial

No evidence of an effect on pain intensity after elective orthopedic or colorectal surgery among elderly people treated with probiotics compared to placebo in a mid-sized RCT¹⁴⁹Wang P, Yin X et al. Perioperative probiotic treatment decreased the incidence of postoperative cognitive impairment in elderly patients following non-cardiac surgery: a randomised double-blind and placebo-controlled trial. Clinical Nutrition. 2021 Jan;40(1):64-71.

Quality of life: preliminary evidence of maintained quality of life scores among home-living adults receiving tube feedings enriched with prebiotics

Maintained quality of life scores among home-living adults receiving tube feedings enriched with fructo-oligosaccharides and fiber compared to declines among people receiving no-residue tube feeding in a small controlled trial¹⁵⁰Wierdsma NJ, van Bodegraven AA et al. Fructo-oligosaccharides and fibre in enteral nutrition has a beneficial influence on microbiota and gastrointestinal quality of life. Scandinavian Journal of Gastroenterology. 2009;44(7):804-12.

Sleep disruption: no evidence of an effect on sleep quality among people treated with probiotics in small trials

No evidence of an effect on sleep quality after elective orthopedic or colorectal surgery among elderly people treated with probiotics compared to placebo in a mid-sized RCT¹⁵¹Wang P, Yin X et al. Perioperative probiotic treatment decreased the incidence of postoperative cognitive impairment in elderly patients following non-cardiac surgery: a randomised double-blind and placebo-controlled trial. Clinical Nutrition. 2021 Jan;40(1):64-71.
No effect on sleep symptoms among people with symptoms of stress treated with a probiotic containing Lactobacillus acidophilus Rosell-52 and Bifidobacterium longum Rosell-175 for 3 weeks compared to placebo in a small RCT¹⁵²Diop L, Guillou S, Durand H. Probiotic food supplement reduces stress-induced gastrointestinal symptoms in volunteers: a double-blind, placebo-controlled, randomized trial. Nutrition Research. 2008 Jan;28(1):1-5.

Stress

No evidence of an effect on stress among people with symptoms of stress treated with probiotics in a combined analysis of studies

Modest evidence of less perceived stress among healthy volunteers treated with probiotics

Preliminary evidence of a lower marker of stress 5 to 7 days after elective orthopedic or colorectal surgery among elderly people treated with probiotics

No evidence of an effect on stress among people with symptoms of stress treated with probiotics compared to placebo in a meta-analysis of 23 controlled trials¹⁵³Zagórska A, Marcinkowska M, Jamrozik M, Wiśniowska B, Paśko P. From probiotics to psychobiotics—the gut-brain axis in psychiatric disorders. Beneficial Microbes. 2020 Dec 2;11(8):717-732.
Lower subjective stress among healthy volunteers treated with probiotics compared to controls in a meta-analysis of 7 RCTs¹⁵⁴Zhang N, Zhang Y et al. Efficacy of probiotics on stress in healthy volunteers: a systematic review and meta-analysis based on randomized controlled trials. Brain and Behavior. 2020 Sep;10(9):e01699.
Fewer symptoms of preclinical perceived stress among healthy volunteers treated with probiotics compared to placebo in a meta-analysis of 7 RCTs¹⁵⁵McKean J, Naug H, Nikbakht E, Amiet B, Colson N. Probiotics and subclinical psychological symptoms in healthy participants: a systematic review and meta-analysis. Journal of Alternative and Complementary Medicine. 2017 Apr;23(4):249-258.
A lower marker of stress (cortisol) 5 to 7 days after elective orthopedic or colorectal surgery among elderly people treated with probiotics compared to placebo in a mid-sized RCT¹⁵⁶Wang P, Yin X et al. Perioperative probiotic treatment decreased the incidence of postoperative cognitive impairment in elderly patients following non-cardiac surgery: a randomised double-blind and placebo-controlled trial. Clinical Nutrition. 2021 Jan;40(1):64-71.

Surgery outcomes

Preliminary evidence of lower incidence of multiorgan failure, septic complications, and mortality among people with severe acute pancreatitis treated with synbiotics

No evidence of an effect on bacterial translocation, gastric colonization, or incidence of sepsis after elective major abdominal surgery among people treated with a probiotic alone

Preliminary evidence of less bacterial overgrowth and higher vitamin B12 levels after Roux-en-Y gastric bypass surgery among people treated with Lactobacillus after surgery

Synbiotics

Preliminary evidence of lower incidence of multiorgan failure, septic complications, and mortality among people with severe acute pancreatitis treated with synbiotics

Less surgical site infection, pneumonia, or sepsis, plus shorter duration of antibiotic administration and hospital stays after surgery (not specific to cancer) among people treated with synbiotic therapy compared to either probiotics or prebiotics alone in a meta-analysis of 31 observationala type of study in which individuals are observed or certain outcomes are measured, but no attempt is made to affect the outcome (for example, no treatment is given); an example is a study that records people’s diets, but doesn’t try to alter their diets, and looks for patterns of disease or other outcomes related to different foods and controlled studies¹⁵⁷Kasatpibal N, Whitney JD et al. Effectiveness of probiotic, prebiotic, and synbiotic therapies in reducing postoperative complications: a systematic review and network meta-analysis. Clinical Infectious Diseases. 2017 May 15;64(suppl_2):S153-S160.
Lower incidence of multiorgan failure, septic complications, and mortality among people with severe acute pancreatitis treated with 4 different Lactobacilli preparations with 1010 CFU and prebiotics containing 4 bioactive fibers (inulin, beta-glucan, resistant starch, and pectin) compared to prebiotics alone in a small RCT¹⁵⁸Oláh A, Belágyi T, Pótó L, Romics L Jr, Bengmark S. Synbiotic control of inflammation and infection in severe acute pancreatitis: a prospective, randomized, double blind study. Hepatogastroenterology. 2007 Mar;54(74):590-4.
Lower incidence of bacterial translocation after bowel mobilization but no evidence of an effect on intestinal permeability, inflammatory response, or sepsis after elective colorectal surgery among people treated with synbiotics, neomycin, and mechanical bowel preparation (MBP) compared to MBP alone or MBP with neomycin in a mid-sized RCT¹⁵⁹Reddy BS, Macfie J et al. Randomized clinical trial of effect of synbiotics, neomycin and mechanical bowel preparation on intestinal barrier function in patients undergoing colectomy. British Journal of Surgery. 2007 May;94(5):546-54.
Fewer infections after liver transplantation among people treated with a fiber-containing formula plus living Lactobacillus plantarum 299 compared to either a fiber-containing formula plus inactivated L plantarum 299 or to standard early enteral nutrition plus selective bowel decontamination in a small RCT¹⁶⁰Rayes N, Seehofer D et al. Early enteral supply of lactobacillus and fiber versus selective bowel decontamination: a controlled trial in liver transplant recipients. Transplantation. 2002 Jul 15;74(1):123-7.
Fewer bacterial infections and shorter duration of antibiotic therapy after liver transplantation among people treated with enteral nutrition enriched with 4 different lactic acid bacteria and 4 fibers starting the day before surgery and continuing for 14 days compared to 4 fibers without Lactobacillus in a small RCT¹⁶¹Rayes N, Seehofer D et al. Supply of pre- and probiotics reduces bacterial infection rates after liver transplantation–a randomized, double-blind trial. American Journal of Transplantation. 2005 Jan;5(1):125-30.
Lower rate of infection, primarily urinary tract infection, after living-donor liver transplantation among people treated with synbiotic therapy comprising Bifidobacterium breve, Lactobacillus casei, and galactooligosaccharides for 2 days before surgery and continuing 2 weeks after surgery compared to controls in a small RCT¹⁶²Eguchi S, Takatsuki M et al. Perioperative synbiotic treatment to prevent infectious complications in patients after elective living donor liver transplantation: a prospective randomized study. American Journal of Surgery. 2011 Apr;201(4):498-502.

Probiotics alone

No evidence of an effect on bacterial translocation, gastric colonization, or incidence of sepsis after elective major abdominal surgery among people treated with a probiotic alone

Preliminary evidence of less bacterial overgrowth and higher vitamin B12 levels after Roux-en-Y gastric bypass surgery among people treated with Lactobacillus after surgery

No evidence of an effect on bacterial translocation, gastric colonization, or incidence of sepsis after elective major abdominal surgery among people treated with an oral preparation containing Lactobacillus plantarum 299v (Proviva) for at least 1 week before surgery and also after surgery compared to controls in a mid-sized RCT¹⁶³McNaught CE, Woodcock NP, MacFie J, Mitchell CJ. A prospective randomised study of the probiotic Lactobacillus plantarum 299V on indices of gut barrier function in elective surgical patients. Gut. 2002 Dec;51(6):827-31.
Less bacterial overgrowth and higher vitamin B12 levels after Roux-en-Y gastric bypass surgery among people treated with Lactobacillus after surgery compared to controls in a small RCT¹⁶⁴Woodard GA, Encarnacion B et al. Probiotics improve outcomes after Roux-en-Y gastric bypass surgery: a prospective randomized trial. Journal of Gastrointestinal Surgery. 2009 Jul;13(7):1198-204.

Probiotics combined with other therapies

Probiotics with glutamine and fish oil: preliminary evidence of lower rates of abdominal pain, flatulence, and diarrhea after completing radiotherapy among people with abdominal or pelvic cancer treated with probiotics, glutamine, and fish oil

Probiotics and electroacupuncture: preliminary evidence of fewer symptoms of depression and diarrhea among people with depression and chronic diarrhea treated with electroacupuncture and probiotics

Reducing cancer risk

Are probiotics and prebiotics linked to lower risks of developing cancer or of recurrence? We present the evidence.

Bladder cancer

Preliminary evidencesignificant effects in small or poorly designed clinical studies OR conflicting results in adequate studies but a preponderance of evidence of an effect (this is the CancerChoices definition; other researchers and studies may define this differently) of lower risk of recurrence among people with superficial transitional cell carcinoma of the bladder treated with an oral probiotic

Lower risk of recurrence among people with superficial transitional cell carcinoma of the bladder after transurethral resection with either primary multiple tumors or recurrent single tumors, but no evidence of an effectoverall, one or more studies did not demonstrate that a treatment or intervention led to an expected outcome; this does not always mean that there is no effect in clinical practice, but that the studies may have been underpowered (too few participants) or poorly designed. Larger, well-designed studies provide more confidence in making assessments. among people with recurrent multiple tumors treated with an oral Lactobacillus casei preparation compared to placeboa pill, medicine, or procedure—thought to be both harmless and ineffective—prescribed for the psychological benefit to the patient or as a sham treatment in a study to allow a comparison to a therapy of interest in a small RCTrandomized controlled trial, a study design in which people are randomly assigned to either an experimental group or a control group to compare the outcomes from different treatments; an RCT is considered a strong design for determining a therapy’s effects¹⁶⁷Aso Y, Akaza H et al. Preventive effect of a Lactobacillus casei preparation on the recurrence of superficial bladder cancer in a double-blind trial. The BLP Study Group. European Urology. 1995;27(2):104-9.
Lower risk of bladder cancer among people eating fermented dairy foods compared to others in a subgroup analysis of a very large meta-analysisa statistical analysis that combines the results of two or more research studies; the results of smaller research studies addressing the same or similar questions can be analyzed as though they are one bigger, more powerful study of 61 observationala type of study in which individuals are observed or certain outcomes are measured, but no attempt is made to affect the outcome (for example, no treatment is given); an example is a study that records people’s diets, but doesn’t try to alter their diets, and looks for patterns of disease or other outcomes related to different foods studies¹⁶⁸Zhang K, Dai H, Liang W, Zhang L, Deng Z. Fermented dairy foods intake and risk of cancer. International Journal of Cancer. 2019 May 1;144(9):2099-2108.

Breast cancer

Preliminary evidence of lower risk of breast cancer among women drinking beverages containing Lactobacillus casei Shirota 4 or more times a week

Colorectal cancer

Preliminary evidence of better epithelial barrier function and a weak trendan apparent change due to a therapy, close to but not achieving full statistical significance (this is the CancerChoices definition; other researchers and studies may define this differently toward lower colorectal proliferation after colorectal polypectomy among people treated with a synbiotic

Good evidence of lower risk of colorectal cancer among people eating fermented dairy foods as a whole

Preliminary evidence of lower atypia grade of tumors and fewer tumors or aberrant crypt foci among people with prior colorectal tumor removal treated with a probiotic dairy product

No evidence of an effectoverall, one or more studies did not demonstrate that a treatment or intervention led to an expected outcome; this does not always mean that there is no effect in clinical practice, but that the studies may have been underpowered (too few participants) or poorly designed. Larger, well-designed studies provide more confidence in making assessments. on the number or size of recurring tumors among people with prior colorectal tumor removal, resected colon, or more than 5 aberrant crypt foci treated with a probiotic or prebiotic in small trials

Synbiotic: preliminary evidence of better epithelial barrier function and a weak trend toward lower colorectal proliferation after colorectal polypectomy among people treated with a synbiotic

Better epithelial barrier function and a weak trend toward lower colorectal proliferation after colorectal polypectomy among people treated with a synbiotic comprising Lactobacillus rhamnosus GG, Bifidobacterium lactis Bb12, and inulin enriched with oligofructose compared to placeboa pill, medicine, or procedure—thought to be both harmless and ineffective—prescribed for the psychological benefit to the patient or as a sham treatment in a study to allow a comparison to a therapy of interest in a small RCTrandomized controlled trial, a study design in which people are randomly assigned to either an experimental group or a control group to compare the outcomes from different treatments; an RCT is considered a strong design for determining a therapy’s effects, but no evidence of an effect among people with colorectal cancer¹⁷⁰Rafter J, Bennett M et al. Dietary synbiotics reduce cancer risk factors in polypectomized and colon cancer patients. American Journal of Clinical Nutrition. 2007 Feb;85(2):488-96.

Probiotic only

Good evidence of lower risk of colorectal cancer among people eating fermented dairy foods as a whole

Preliminary evidence of lower atypia grade of tumors and fewer tumors or aberrant crypt foci among people with prior colorectal tumor removal treated with a probiotic dairy product

No evidence of an effect on the number or size of recurring tumors among people with prior colorectal tumor removal treated with a probiotic in a mid-sized trial

Lower risk of colorectal cancer among people eating fermented dairy foods compared to others in a subgroup analysis of a very large meta-analysisa statistical analysis that combines the results of two or more research studies; the results of smaller research studies addressing the same or similar questions can be analyzed as though they are one bigger, more powerful study of 61 observationala type of study in which individuals are observed or certain outcomes are measured, but no attempt is made to affect the outcome (for example, no treatment is given); an example is a study that records people’s diets, but doesn’t try to alter their diets, and looks for patterns of disease or other outcomes related to different foods studies¹⁷¹Zhang K, Dai H, Liang W, Zhang L, Deng Z. Fermented dairy foods intake and risk of cancer. International Journal of Cancer. 2019 May 1;144(9):2099-2108.
Lower atypia grade of tumors (adenomas and/or early cancers) and fewer tumors at least 4 mm in size but less than 10 mm at 2 years—but not 4 years—among people with at least 2 colorectal tumors removed previously and treated with a probiotic dairy product containing L. casei compared to no treatment or wheat bran in a mid-sized RCT¹⁷²Ishikawa H, Akedo I et al. Randomized trial of dietary fiber and Lactobacillus casei administration for prevention of colorectal tumors. International Journal of Cancer. 2005 Sep 20;116(5):762-7.
No evidence of an effect on the number or size of recurring tumors among people with at least 2 colorectal tumors removed previously and treated with a probiotic dairy product containing L. casei for 4 years compared to no treatment or wheat bran in a mid-sized RCT¹⁷³Ishikawa H, Akedo I et al. Randomized trial of dietary fiber and Lactobacillus casei administration for prevention of colorectal tumors. International Journal of Cancer. 2005 Sep 20;116(5):762-7.

Prebiotic only: no evidence of an effect on the number of aberrant crypt foci—a risk factor for colorectal cancer— among people with prior resected colon or more than 5 aberrant crypt foci treated with a prebiotic in a small trial

No evidence of an effect on the number of aberrant crypt foci after 6 months among people with either previously resected colon cancer or more than 5 aberrant crypt foci discovered on colonoscopy treated with the prebiotic oligofructose-enriched inulin compared to sulindac, atorvastatin, or placebo in a small RCT¹⁷⁴Limburg PJ, Mahoney MR et al; Cancer Prevention Network. Randomized phase II trial of sulindac, atorvastatin, and prebiotic dietary fiber for colorectal cancer chemoprevention. Cancer Prevention Research (Philadelphia, PA). 2011 Feb;4(2):259-69.

Gastrointestinal cancer

Colorectal cancer is listed separately.

Good evidence of lower risk of esophageal cancer among people eating fermented dairy foods (yogurt, kefir)

Keep reading about probiotics and prebiotics

See all our reviews of complementary therapies

Author

Nancy Hepp, MS

Lead Researcher

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Andrew Jackson, ND

Research Associate

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Reviewer

Laura Pole, MSN, RN, OCNS

Senior Clinical Consultant

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Last update: January 31, 2024

Last full literature review: November 2022

CancerChoices provides information about integrativein cancer care, a patient-centered approach combining the best of conventional care, self care, and evidence-informed complementary care in an integrated plan cancer care. We review complementaryin cancer care, complementary care involves the use of therapies intended to enhance or add to standard conventional treatments; examples include supplements, mind-body approaches such as yoga or psychosocialtherapy, and acupuncture therapies and self carelifestyle actions and behaviors that may impact cancer outcomes; examples include eating health-promoting foods, limiting alcohol, increasing physical activity, and managing stress practices to help patients and professionals explore and integrate the best combination of conventionalthe cancer care offered by conventionally trained physicians and most hospitals; examples are chemotherapy, surgery, and radiotherapy and complementary therapies and practices for each person.

Our staff have no financial conflicts of interest to declare. We receive no funds from any manufacturers or retailers gaining financial profit by promoting or discouraging therapies mentioned on this site.

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