Intermittent Fasting: New Review Questions Popular Weight Loss Method

A major new review has cast doubt on the effectiveness of intermittent fasting as a weight loss strategy, finding it may make "little to no difference" compared to traditional dieting methods or no intervention at all.

The research, published in the Cochrane Database of Systematic Reviews, analyzed data from 22 previous studies involving nearly 2,000 overweight or obese adults who tried various forms of intermittent fasting over periods up to 12 months.

What the Research Found

Intermittent fasting encompasses several approaches, including:

• The 5:2 diet (eating normally five days, restricting calories two days)
• Time-restricted eating (consuming all meals within an 8-hour window)
• Alternating between normal eating days and very low-calorie days

When compared to standard dietary advice like reducing calorie intake and eating more healthily, the review found intermittent fasting produced "little to no difference" in weight loss outcomes. The same was true when comparing fasting to those who received no weight loss advice at all.

Lead author Luis Garegnani from the Universidad Hospital Italiano de Buenos Aires expressed concern about the online hype surrounding fasting. "Intermittent fasting may be a reasonable option for some people, but the current evidence doesn't justify the enthusiasm we see on social media," he said.

Why the Results Are Complicated

Researchers noted several limitations in the existing evidence. Most studies used methods that weren't the most robust, and many involved relatively small numbers of participants. This makes it difficult to determine the true effects of intermittent fasting on weight loss.

The team expressed "moderate confidence" in their overall findings but were less certain when comparing standard dieting directly with intermittent fasting approaches.

Potential Health Benefits Beyond Weight

While the review questions intermittent fasting's effectiveness for weight loss, researchers suggest it might still offer health benefits through positive changes to certain body functions. However, they emphasize that more evidence is needed to confirm these potential advantages.

The review also highlighted the need for more research on how different types of intermittent fasting affect:

• Men and women separately
• People with different body mass indexes
• Individuals from various countries and cultural backgrounds
• Those with underlying health conditions like type 2 diabetes

Expert Reactions

Dr. Baptiste Leurent, associate professor in medical statistics at University College London, said the studies "provide a clear indication that intermittent fasting offers little benefit" and represents "yet another example of a misalignment between public perception and the scientific evidence."

Prof. Keith Frayn, emeritus professor of human metabolism at the University of Oxford, noted that intermittent fasting has been widely promoted based on claims of "special effects on metabolism." He stated the study shows "such claims can have little relevance" and emphasized there are no "quick fixes" for weight loss beyond reducing calorie intake.

What This Means for People Trying to Lose Weight

Senior review author Eva Madrid emphasized that weight loss approaches should be personalized. "Doctors will need to take a case-by-case approach when advising an overweight adult on losing weight," she said.

The researchers acknowledge that individual responses to intermittent fasting vary, and some people may still find it beneficial for weight maintenance or other health reasons not captured in this review.

Context: Weight Loss Trends

This review comes as weight loss drugs like Wegovy and Mounjaro have gained popularity, with around 1.6 million adults in the UK using these injections. However, a recent study found that people who stop using these weight loss medications can regain weight four times faster than those who stop conventional dieting and exercise.

While intermittent fasting remains popular on social media and in wellness circles, this comprehensive review suggests the scientific evidence supporting its superiority for weight loss may be overstated. The researchers call for more rigorous studies to better understand both the benefits and limitations of various fasting approaches.

The findings reinforce that sustainable weight management likely requires individualized approaches focused on overall calorie balance and healthy eating patterns, rather than relying on any single "magic bullet" method.