Calorie restriction and fasting, whether for 12 or more hours every night or occasionally for longer periods, can contribute to lower body weight, blood sugar, and insulin resistance, plus fewer unpleasant chemotherapy-related side effects.

How can fasting or calorie restriction 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.

Improving treatment outcomes

Is fasting or calorie restriction linked to improved survival? Is it linked to less cancer growth or metastasis? Does it enhance the anticancer action of other treatments or therapies? We present the evidence.

Breast 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 higher tumor response rates among nondiabetic women with stage 2 or 3 HER-2 negative breast cancer eating a fasting-mimicking diet for 3 days before and during neoadjuvanttherapy used before a main treatment, such as chemotherapy, radiation therapy, and hormone therapy before surgery chemotherapy

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 cancer-specific or all-cause mortality among nondiabetic women with early stage breast cancer fasting 13 or more hours per night in a large study

Gynecologic cancer

Dose reductions or delays are not in themselves indicators of treatment outcomes, but we report them here because completing treatment is directly related to better treatment outcomes.

Preliminary evidence of fewer reported dose reductions or delays in chemotherapy among people with gynecologic cancer following a water-only fast 24 hours before and 24 hours after chemotherapy

Fasting combined with other therapies

Fasting combined with a calorie-restricted ketogenic diet: preliminary evidence of better survival among people with malignant glioma achieving a blood glucose level less than the median by fasting in addition to eating a calorie-restricted ketogenic diet

Optimizing your body terrain

Does fasting or calorie restriction 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

This evidence is not specific to people with cancer.

Strong evidenceconsistent, significant effects in several large (or at least one very large) well designed clinical studies or at least two meta-analyses of clinical studies of moderate or better quality (or one large meta-analysis) finding similar results (this is the CancerChoices definition; other researchers and studies may define this differently) of more weight loss and less body fat among people fasting, usually for 24 hours at a time

Strong evidence of more weight loss and less body fat among people restricting calorie intake

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 more weight loss and less body fat among overweight people exercising to create an energy deficit of about 20%

Preliminary evidence of more weight loss and less body fat among overweight people exercising to create an energy deficit of about 12.5% and exercising to increase total energy expenditure by 12.5%

High blood sugar and insulin resistance

This evidence is not specific to people with cancer.

The study authors do not always report whether the people in their study had elevated blood sugar, insulin, or insulin resistance at the start of the study. If these measures were not elevated at the start, we wouldn’t expect to see much decrease during the study. 

Modest (and somewhat conflicting) 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 (glucose) or insulin levels or lower 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 predominantly overweight or obese people fasting for several hours to 24 hours

Preliminary (and somewhat conflicting) evidence of lower blood sugar, insulin, and insulin resistance among people restricting calorie intake

Preliminary evidence of better insulin sensitivity and glucose tolerance among normal weight or overweight, nondiabetic people exercising to create a 16% energy deficit

Preliminary evidence of more insulin sensitivity among nondiabetic, overweight people creating energy deficits by both restricting calories and exercising

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.

This evidence is not specific to people with cancer.

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 levels of insulin-like growth factor-1 (IGF-1)—higher levels are linked to higher risk of cancer and worse outcomes—among people fasting or restricting calories by more than 30% but not among people restricting calories by 30% or less

Preliminary evidence of lower total and free IGF-1 among people restricting protein intake

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 higher adiponectin levels among people fasting but no evidence of an effect from restricting calories

Preliminary evidence of lower serum T3 levels and energy intake but no evidence of an effect on serum total T4, free T4, reverse T3, and TSH levels among healthy adults participating in long-term calorie restriction

Modest evidence of lower levels of leptin, a hormone that helps regulate energy balance by inhibiting hunger, among overweight or obese people fasting or restricting calories

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 levels of the “hunger hormone” ghrelin among nonobese, nondiabetic adults fasting every other day in a small study

Preliminary evidence of comparable reductions in free androgen index among generally healthy, overweight or obese women achieving overall 25% weekly calorie restriction either by fasting or restricting daily calories

Inflammation

No evidence of an effect on markers of inflammation among people fasting in several small studies

Preliminary (and conflicting) evidence of lower markers of inflammation among people restricting calories

Oxidative stress

Preliminary evidence of less 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 predominantly overweight or obese people fasting or restricting eating

Your microbiome

Preliminary evidence of favorable changes in the gut microbiota among adults with metabolic syndromea cluster of conditions that occur together, including increased blood pressure, high blood sugar, excess body fat around the waist, and abnormal cholesterol or triglyceride levels restricting calories

Tissue and organ regeneration

Preliminary evidence of a higher marker of adult tissue and organ regeneration among healthy adults restricting calories periodically

Managing side effects and promoting wellness

Is fasting or calorie restriction linked to fewer or less severe side effects or symptoms? Is it linked to less toxicity from cancer treatment? Does it support your quality of life or promote general well-being? We present the evidence.

Side effects as a whole

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 fewer chemotherapy-related side effects among people with gynecologic cancer fasting before and after chemotherapy

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 chemotherapy-related side effects not related to blood (non-hematological toxicity) among women with breast cancer fasting before and after chemotherapy

Blood-related side effects

Preliminary evidence of less blood-related toxicity among people with breast cancer fasting before and after chemotherapy

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 less chemotherapy-induced DNA damage in leukocytes among people with cancer fasting either before or both before and after platinum-based chemotherapy without concurrent radiation

Preliminary evidence of less chemotherapy-induced DNA damage in T-lymphocytes among women with breast cancer eating a fasting-mimicking diet for 3 days before or during neoadjuvanttherapy used before a main treatment, such as chemotherapy, radiation therapy, and hormone therapy before surgery chemotherapy

Cardiovascular side effects

Weak evidence of lower risk of cardiovascular disease 1 to 6 years after completing cardiotoxic cancer treatment (anthracyclines) among cardiometabolically unhealthy, overweight or obese people with breast cancer participating in 16 hours of fasting every night

Fatigue

Preliminary evidence of less fatigue among people with cancer fasting or restricting calories before and/or after chemotherapy treatments

Gastrointestinal side effects

Preliminary evidence of less nausea and other gastrointestinal side effects among people with cancer fasting or restricting calories before and/or after chemotherapy treatments

Quality of life and physical function

Preliminary and somewhat conflicting evidence of better quality of life scores among people with gynecologic or breast cancer fasting before and/or after chemotherapy treatments

Weak evidence of less weakness from chemotherapy among people with cancer fasting before and/or after chemotherapy treatments

Sleep disruption

Preliminary evidence of better sleep among people with breast cancer fasting before chemotherapy treatment

Preliminary evidence of longer sleep among people with breast cancer fasting more hours every night

Hospital admission

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 hospital admission among people with gynecologic cancer fasting before and after chemotherapy treatment

Symptoms not specific to cancer

Cardiovascular symptoms

Preliminary evidence of lower blood pressure among generally healthy people (not specific to cancer) fasting at least 14 hours a day

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 pressure among people (not specific to cancer) fasting periodically or restricting calories

No evidence of an effect on blood pressure among people (not specific to cancer) severely restricting calories on alternate days for 4 weeks and then resuming unrestricted eating for 8 weeks in a small study

Sleep disruption

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 sleep quality among people (not specific to cancer) fasting 14 to 16 hours every night

Calorie restriction combined with other therapies

Calorie restriction, behavioral therapy, and exercise leading to 30 pounds or more of weight loss: modest evidence of fewer self-reported symptoms of depression among people with symptoms participating in calorie restriction, behavioral therapy, and exercise leading to 30 pounds or more of weight loss

Reducing cancer risk

Is fasting or calorie restriction linked to lower risks of developing cancer or of recurrence? We present the evidence.

Breast 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 higher risk of recurrence among nondiabetic women with early stage breast cancer fasting less than 13 hours every night

Helpful links

Fasting Frenzy: The Science behind Fasting and What to Consider before Beginning Intermittent Fasting: Risks, Benefits, and Why It’s Not for Everyone From Anticancer Lifestyle Program

Play video

Keep reading about fasting or calorie restriction

Author

Nancy Hepp, MS

Lead Researcher
View profile

Ms. Hepp is a researcher and communicator who has been writing and editing educational content on varied health topics for more than 20 years. She serves as lead researcher and writer for CancerChoices and also served as the first program manager. Her graduate work in research and cognitive psychology, her master’s degree in instructional design, and her certificate in web design have all guided her in writing and presenting information for a wide variety of audiences and uses. Nancy’s service as faculty development coordinator in the Department of Family Medicine at Wright State University also provided experience in medical research, plus insights into medical education and medical care from the professional’s perspective.

Nancy Hepp, MS Lead Researcher

Reviewer

Susan Yaguda, MSN, RN

Manager at Atrium Health’s Levine Cancer Institute and CancerChoices Clinical Consultant
View profile

Susan Yaguda, MSN, RN, has been a nurse for nearly 40 years, working in a variety of healthcare settings. She currently works in Charlotte, North Carolina, at Atrium Health’s Levine Cancer Institute as the manager for Integrative Oncology and Cancer Survivorship. She works with a multidisciplinary team to deliver holistic, evidence-based support and education for patients and care partners at any point along the trajectory of cancer care. She completed the Integrative Oncology Scholars Program through the University of Michigan in 2020, is certified as an Integrative Health Coach through Duke Integrative Medicine and has a post-graduate certificate in Nursing Education from the University of North Carolina, Charlotte. Susan also was awarded the Planetree International Scholar’s Award in 2018 and was recognized by the Daisy Foundation for Nurse Leadership in 2021. Susan has a particular interest in empowering patients and care partners with knowledge to help drive informed decision making and educating nurses on the benefits of integrative care for patients and self-care. She has presented nationally and internationally on integrative oncology and nursing education.

She and her husband, Mark, have two adult children and a very spoiled foxhound. She enjoys hiking, knitting, cooking, and pickleball.

“As a frequent consumer of Beyond Conventional Cancer Therapies, and now CancerChoices, for both professional education and patient support, it is an honor to have the opportunity to engage with the dedicated team at CancerChoices to serve those impacted by this disease.”  

 

Susan Yaguda, MSN, RN Manager at Atrium Health’s Levine Cancer Institute and CancerChoices Clinical Consultant

Last update: May 9, 2024

Last full literature review: April 2023

We are grateful for research support from Dr. Irfan Siddique and Adriana Gutierrez Galvis.

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.

Learn more

References[+]