Health effects of intermittent fasting: hormesis or harm? A systematic review

Am J Clin Nutr. 2015 Aug;102(2):464-70. doi: 10.3945/ajcn.115.109553. Epub 2015 Jul 1.


Background: Intermittent fasting, alternate-day fasting, and other forms of periodic caloric desistance are gaining popularity in the lay press and among animal research scientists. Whether clinical evidence exists for or is strong enough to support the use of such dietary regimens as health interventions is unclear.

Objective: This review sought to identify rigorous, clinically relevant research studies that provide high-quality evidence that therapeutic fasting regimens are clinically beneficial to humans.

Design: A systematic review of the published literature through January 2015 was performed by using sensitive search strategies to identify randomized controlled clinical trials that evaluated the effects of fasting on either clinically relevant surrogate outcomes (e.g., weight, cholesterol) or actual clinical event endpoints [e.g., diabetes, coronary artery disease (CAD)] and any other studies that evaluated the effects of fasting on clinical event outcomes.

Results: Three randomized controlled clinical trials of fasting in humans were identified, and the results were published in 5 articles, all of which evaluated the effects of fasting on surrogate outcomes. Improvements in weight and other risk-related outcomes were found in the 3 trials. Two observational clinical outcomes studies in humans were found in which fasting was associated with a lower prevalence of CAD or diabetes diagnosis. No randomized controlled trials of fasting for clinical outcomes were identified.

Conclusions: Clinical research studies of fasting with robust designs and high levels of clinical evidence are sparse in the literature. Whereas the few randomized controlled trials and observational clinical outcomes studies support the existence of a health benefit from fasting, substantial further research in humans is needed before the use of fasting as a health intervention can be recommended.

Keywords: alternate-day fasting; caloric restriction; cognitive performance; coronary artery disease; diabetes; energy restriction; intermittent fasting; obesity; time-restricted feeding; total caloric desistance.

Publication types

  • Meta-Analysis
  • Research Support, Non-U.S. Gov't
  • Review
  • Systematic Review

MeSH terms

  • Adult
  • Animals
  • Caloric Restriction / adverse effects
  • Cognitive Dysfunction / epidemiology
  • Cognitive Dysfunction / prevention & control
  • Coronary Artery Disease / epidemiology
  • Coronary Artery Disease / etiology
  • Coronary Artery Disease / prevention & control
  • Diabetes Mellitus, Type 2 / epidemiology
  • Diabetes Mellitus, Type 2 / etiology
  • Diabetes Mellitus, Type 2 / prevention & control
  • Diet Fads / adverse effects
  • Diet, Reducing / adverse effects*
  • Evidence-Based Medicine*
  • Fasting / adverse effects*
  • Health Status*
  • Hormesis*
  • Humans
  • Hypercholesterolemia / epidemiology
  • Hypercholesterolemia / etiology
  • Hypercholesterolemia / prevention & control
  • Obesity / diet therapy*
  • Obesity / physiopathology
  • Observational Studies as Topic
  • Overweight / diet therapy*
  • Overweight / physiopathology
  • Overweight / prevention & control
  • Randomized Controlled Trials as Topic
  • Risk Factors