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.
References