TLDR
Fasting may help control weight and reduce some treatment side effects, but it has not been proven to prevent cancer or improve survival. People receiving cancer treatment should only fast within a clinical trial, because it may sometimes cause harm.
Summary
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1 Study Aim
The authors review whether intermittent fasting (IF), meaning repeated periods of little or no calorie intake, can prevent cancer or improve treatment outcomes. They compare IF with chronic calorie restriction (CR), meaning eating fewer calories every day. The review also examines fasting-mimicking diets (FMDs), which provide very few calories while resembling fasting. The authors assess biological explanations, animal evidence, human studies, treatment safety, and research gaps. The review asks whether fasting itself helps against cancer, beyond any benefits from losing weight.
2 Study Design
This narrative review evaluates studies in rodents, humans without cancer, cancer patients, and cancer survivors. It discusses alternate-day fasting, weekly fasting, time-restricted feeding (TRF), which limits eating to a daily window, prolonged fasting, and FMDs. The evidence includes laboratory experiments, tumor models, observational studies, feasibility studies, case series, pilot studies, and randomized clinical trials (studies assigning participants to different treatments by chance). Human cancer studies were generally small and varied in their fasting schedules, cancer types, and treatments. The review combines animal experiments with early clinical evidence rather than presenting a new patient trial.
3 Findings
The authors report that IF studies in rodents have mixed results. Some mouse studies showed slower tumor growth, fewer metastases, or better treatment responses, while rat studies sometimes found more aggressive liver or colon cancer after fasting and refeeding. Human evidence does not establish effects on cancer incidence, recurrence, progression, or survival. Short fasting studies during chemotherapy appeared feasible and sometimes reduced side effects, but benefits were inconsistent. A 131-person breast cancer trial found no difference in severe treatment toxicity with an FMD, although tumor response measures favored better adherence. The authors recommend IF for weight management only when appropriate, and advise against fasting during active treatment outside clinical trials. They call for larger, well-designed studies. Fasting may reduce treatment discomfort, but its cancer benefits and risks remain uncertain.