Intermittent fasting diets have become very popular in the past few years, as they can produce clinically significant weight loss. These diets can be defined, in the simplest of terms, as periods of fasting alternating with periods of eating. The most studied forms of intermittent fasting include: alternate day fasting (0–500 kcal per ‘fast day’ alternating with ad libitum intake on ‘feast days’); the 5:2 diet (two fast days and five feast days per week) and time-restricted eating (only eating within a prescribed window of time each day). Despite the recent surge in the popularity of fasting, only a few studies have examined the health benefits of these diets in humans. The goal of this Review is to summarize these preliminary findings and give insights into the effects of intermittent fasting on body weight and risk factors for cardiometabolic diseases in humans. This Review also assesses the safety of these regimens, and offers some practical advice for how to incorporate intermittent fasting diets into everyday life. Recommendations for future research are also presented.
The three main forms of intermittent fasting (alternate day fasting, the 5:2 diet and time-restricted eating) produce mild to moderate weight loss (3–8% loss from baseline) over short durations (8–12 weeks).
The degree of weight loss achieved with intermittent fasting is on a par with that achieved with traditional dieting approaches (daily calorie restriction).
The ability of these intermittent fasting protocols to help to manage weight long-term is still poorly understood, as the majority of studies to date have run for short durations.
Some studies demonstrate that intermittent fasting improves cardiometabolic risk factors such as blood pressure, levels of LDL cholesterol and triglycerides, insulin resistance and HbA1c, while others show no benefit on these parameters.
Intermittent fasting is generally safe and produces few gastrointestinal, neurological, hormonal or metabolic adverse effects.
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The authors thank the participants in the trials discussed in this Review for their time and effort. The authors acknowledge support from the National Institute of Diabetes and Digestive and Kidney Diseases (grant no. R01DK119783). The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health.
K.A.V. received author fees from Hachette Book Group for the book, The Every Other Day Diet. The other authors declare no competing interests.
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Varady, K.A., Cienfuegos, S., Ezpeleta, M. et al. Clinical application of intermittent fasting for weight loss: progress and future directions. Nat Rev Endocrinol 18, 309–321 (2022). https://doi.org/10.1038/s41574-022-00638-x
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