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.

Safety and precautions

Fasting among people without malnutrition or low body mass index (below 18.5) is generally considered safe, with some cautions noted below. 

Fasting before and/or after chemotherapy does not necessarily lead to unintended weight loss. Most studies of fasting have excluded people who are underweight. 

  • No greater weight loss among people with gynecologic malignancy receiving at least 6 cycles of chemotherapy following a water-only fast 24 hours before and 24 hours after chemotherapy compared to nonfasting controls 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 effects1Riedinger CJ, Kimball KJ et al. Water only fasting and its effect on chemotherapy administration in gynecologic malignancies. Gynecologic Oncology. 2020 Dec;159(3):799-803.

Side effects

“Fasting was well tolerated and no serious fasting-related adverse effects were reported” in a large observational study not specific to cancer.2Michalsen A, Hoffmann B et al. Incorporation of fasting therapy in an integrative medicine ward: evaluation of outcome, safety, and effects on lifestyle adherence in a large prospective cohort study. Journal of Alternative and Complementary Medicine. 2005 Aug;11(4):601-7. Common fasting-related side effects include fatigue, headache, and dizziness.3Dorff TB, Groshen S et al. Safety and feasibility of fasting in combination with platinum-based chemotherapy. BMC Cancer. 2016;16:360. More serious side effects are possible among people with diabetes or muscle loss (sarcopenia); some adaptations can avert serious side effects.

Among people with type 2 diabetes, fasting may bring a risk of low blood sugar (hypoglycemia). Patient education and medication reduction has led to fewer hypoglycemic events than expected.4Corley BT, Carroll RW et al. Intermittent fasting in Type 2 diabetes mellitus and the risk of hypoglycaemia: a randomized controlled trial. Diabetic Medicine. 2018 May;35(5):588-594.

Loss of aerobic capacity and lower extremity muscle volume and strength5Weiss EP, Racette SB et al; Washington University School of Medicine CALERIE Group. Lower extremity muscle size and strength and aerobic capacity decrease with caloric restriction but not with exercise-induced weight loss. Journal of Applied Physiology (1985). 2007 Feb;102(2):634-40. or general muscle loss (sarcopenia)6Caccialanza R, Cereda E, De Lorenzo F, Farina G, Pedrazzoli P; AIOM-SINPE-FAVO Working Group. To fast, or not to fast before chemotherapy, that is the question. BMC Cancer. 2018 Mar 27;18(1):337. has been noted among people participating in calorie restriction but not with exercise-induced weight loss or a combination of fasting and exercise.7Bhutani S, Klempel MC, Kroeger CM, Trepanowski JF, Varady KA. Alternate day fasting and endurance exercise combine to reduce body weight and favorably alter plasma lipids in obese humans. Obesity (Silver Spring). 2013 Jul;21(7):1370-9; Weiss EP, Racette SB et al; Washington University School of Medicine CALERIE Group. Lower extremity muscle size and strength and aerobic capacity decrease with caloric restriction but not with exercise-induced weight loss. Journal of Applied Physiology (1985). 2007 Feb;102(2):634-40. Similarly, loss of bone mineral density has been seen among people participating in calorie restriction but not with exercise-induced weight loss.8Villareal DT, Fontana L et al. Bone mineral density response to caloric restriction-induced weight loss or exercise-induced weight loss: a randomized controlled trial. Archives of Internal Medicine. 2006 Dec 11-25;166(22):2502-10. 

In one study, worse sleep efficiencythe ratio of total sleep time to time in bed and sleep latencythe length of time to transition from full wakefulness to sleep were seen, although no effects on self-reported sleep quality, among overweight or obese adults restricting eating to an 8-hour time window, but no restrictions on eating within that window, for 12 weeks compared to baseline or compared to people eating 3 structured meals per day in a mid-sized 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.9Lowe DA, Wu N et al. Effects of time-restricted eating on weight loss and other metabolic parameters in women and men with overweight and obesity: the TREAT randomized clinical trial. JAMA Internal Medicine. 2020 Nov 1;180(11):1491-1499.

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Author

Nancy Hepp, MS

Lead Researcher
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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
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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.

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