In-Human Studies

There are no in-human studies that have evaluated the effect of IF on cancer incidence, so it is unknown whether adopting a regular pattern of IF would decrease the risk of cancer.

Continue Reading

Several in-human studies have evaluated the effect of IF on the efficacy and safety of chemotherapy. In a systematic review, several studies were identified that included fasting cycles of 24 to 180 hours.5 These studies demonstrated lower rates of toxicity, including hematologic toxicity, compared with patients who did not undergo fasting.

A case series published in 2009 followed 6 evaluable patients with cancer who fasted for 24 to 72 hours prior to and/or after chemotherapy and found that self-reported adverse effects were lower when the patients fasted compared with when they did not fast.6

Related Articles

In another study, 13 patients with HER2-negative, stage II/III breast cancer who were planned to receive neoadjuvant or adjuvant docetaxel, doxorubicin, and cyclophosphamide were randomly assigned to undergo short-term fasting (STF) or normal eating before and after chemotherapy.7 Hematologic toxicities where significantly lower in the STF group, with higher mean erythrocyte and thrombocyte counts 7 days after chemotherapy (P = .007 and P = .00007, respectively). There were no differences in nonhematologic toxicities. The study also found that DNA damage recovery of peripheral blood mononuclear cells was increased or occurred more quickly from patients who fasted compared with those who did not.

In a study of 20 patients undergoing platinum-based chemotherapy, the feasibility and safety of fasting for 24, 48, or 72 hours before or after chemotherapy was examined.8 Fasting was determined to be feasible, and the toxicities that occurred were grade 2 or lower. These adverse events included fatigue, headache, and dizziness. DNA damage was significantly reduced in leukocytes among patients who fasted for 48 or 72 hours compared with those who fasted only 24 hours (P = .08). There was a trend toward fewer instances of neutropenia of grade 3/4 among patients who fasted for 48 or 72 hours compared with those who abstained from food for 24 hours, but these data were not statistically significant (P = .17). Fasting reduced IGF-1 levels by 30%, 33%, and 8% in the 24-, 48-, and 72-hour fasting groups, respectively.

An individually randomized, crossover study of 34 patients with gynecologic cancer evaluated a 60-hour fasting period, which included 36 hours of fasting prior to chemotherapy and continued to 24 hours after chemotherapy administration, evaluated quality of life (QoL).9

Adverse effects associated with fasting were low grade and included headache, hunger, nausea, and one orthostatic reaction. There were no significant changes in patient body weight during the study. Fasting maintained QoL, with a decrease that was less than the Minimally Important Difference (MID) as measured by the Functional Assessment of Cancer Therapy-General (FACT-G) scale compared with a significant decrease during nonfasting periods. As measured by the Functional Assessment of Chronic Illness Therapy (FACIT) scales, chemotherapy-induced deterioration was lower in patients during the fasting period compared with the nonfasting period.


Current data in humans suggests that IF may be beneficial for chemotherapy outcomes, particularly for reducing toxicities. IF appears to be safe in appropriately selected patients, and the adverse effects associated with fasting appear to all be of low grade. However, IF has not yet been studied in large, randomized controlled trials, and therefore, definitive conclusions regarding the approach’s safety and efficacy in cancer prevention and treatment cannot be made at this time.


  1. Mattson MP, Longo VD, Harvie M. Impact of intermittent fasting on health and disease processes. Ageing Res Rev. 2017;39:46-58.
  2. Brandhorst S, Longo VD. Fasting and caloric restriction in cancer prevention and treatment. Recent Results Cancer Res. 2016;207:241-266.
  3. Caccialanza R, Cereda E, De Lorenzo F, Farina G, Pedrazzoli P; the AIOM-SINPE-FAVO Working Group. To fast, or not to fast before chemotherapy, that is the question. BMC Cancer. 2018;18:337-341.
  4. Sun L, Li Y-J, Yang X, Gao L, Yi C. Effect of fasting therapy in chemotherapy-protection and tumor suppression: a systematic review. Transl Cancer Res. 2017;6:354-365. doi: 10.21037/tcr.2017.03.35
  5. Lv M, Zhu X, Wang H, Wang F, Guan W. Roles of caloric restriction, ketogenic diet and intermittent fasting during initiation, progression and metastasis of cancer in animal models: a systematic review and meta-analysis. PLoS ONE. 2014;9(12):e115147.
  6. Safdie FM, Dorff T, Quinn D, et al. Fasting and cancer treatment in humans: a case series report. Aging (Albany NY). 2009;1(12):988-1007.
  7. de Groot S, Vreeswijk MPG, Welters MJP, et al. The effects of short-term fasting on tolerance to (neo) adjuvant chemotherapy in HER2-negative breast cancer patients: a randomized pilot study. BMC Cancer. 2015;15:652.
  8. Dorff TB, Groshen S, Garcia A, et al. Safety and feasibility of fasting in combination with platinum-based chemotherapy. BMC Cancer. 2016;16:360.
  9. Bauersfeld SP, Kessler CS, Wischnewsky M, et al. The effects of short-term fasting on quality of life and tolerance to chemotherapy in patients with breast and ovarian cancer: a randomized cross-over pilot study. BMC Cancer. 2018;18(1):476.