Intermittent Fasting: New Research Shows Limited Weight Loss Benefits

A new systematic review published in the Cochrane Database of Systematic Reviews challenges the popular notion that intermittent fasting is a superior weight loss strategy. The research, involving 22 randomized controlled trials, suggests that intermittent fasting offers only a small benefit compared to simply doing nothing, and no benefit when compared to standard dietary advice.

What the Experts Say

Dr. Baptiste Leurent, Associate Professor in Medical Statistics at University College London, described the review as “a extremely well conducted review, with a robust methodology and appropriate interpretation from the authors.” He emphasized that Cochrane reviews are considered the “gold standard” in evaluating health interventions. According to Dr. Leurent, the review found “absolutely no benefit of intermittent fasting on weight loss, when compared to standard dietary advice,” but a small, statistically significant reduction of 2 to 5% in weight after 6 to 12 months when compared to no intervention.

Professor Keith Frayn, Emeritus Professor of Human Metabolism at the University of Oxford, agreed, stating the review is “very authoritative” and finds no evidence that intermittent fasting is better than regular dietary advice for weight loss. He noted that claims of special metabolic effects beyond calorie restriction appear to be unsubstantiated.

Professor Paul Garner, Emeritus Professor at the Liverpool School of Tropical Medicine, highlighted that the studies examined focused on intermittent fasting recommended by doctors, not individuals self-selecting the diet. He cautioned that the results may not apply to highly motivated individuals who choose to practice intermittent fasting on their own.

Dr. Adam Collins, Associate Professor of Nutrition at the University of Surrey, cautioned against interpreting the findings as a complete dismissal of intermittent fasting. He explained that many studies compare intermittent fasting to continuous energy restriction (CER), where participants reduce calorie intake daily, and that intermittent fasting regimens often create a similar calorie deficit. He also pointed to the potential “Hawthorne effect,” where participants change their behavior simply by being observed in a study.

Understanding the Different Types of Intermittent Fasting

According to Professor Leonie Heilbronn, PhD, Group Leader, Obesity and Metabolism, Adelaide University, it’s important to distinguish between different types of intermittent fasting. She explains that time-restricted eating (TRE), involving a 2-3 hour eating window, is a milder intervention resulting in modest weight loss. Alternate-day fasting (ADF), with significant energy restriction for 2-3 days per week, is more intense and typically shows similar weight loss to moderate continuous calorie restriction.

Key Findings and Clinical Significance

The review found that intermittent fasting resulted in about 3.4% greater weight loss than a control group, which Professor Heilbronn considers potentially clinically meaningful, aligning with guidelines from the National Institute for Health and Care Excellence (NICE) which consider 3% weight loss meaningful.

The Bottom Line

Whereas intermittent fasting may offer a small benefit over doing nothing, the evidence suggests it is not superior to standard dietary advice for weight loss. The researchers emphasize the need for more research, particularly focusing on highly motivated individuals and the potential metabolic benefits beyond weight loss. As Professor Frayn concludes, reducing calorie intake remains the key to weight loss, and there are no “quick fixes.”

Further Information

You can find the original research in the Cochrane Database of Systematic Reviews. Baptiste Leurent’s profile is available on ORCID.