Intermittent fasting doesn’t seem to be more effective for weight loss compared to standard diets, and it’s only slightly better than doing nothing at all, according to a significant review of research.
Researchers examined data from 22 studies worldwide and discovered that people who are overweight or obese experienced similar weight loss results whether they followed conventional dietary guidelines or engaged in fasting methods like the well-known 5:2 diet, which gained popularity through the work of the late Michael Mosley.
The findings suggest that intermittent fasting is almost no more effective for weight loss than not dieting, with individuals losing roughly 3% of their body weight through fasting—well below the 5% that experts consider to be important. It’s worth noting that all the studies had a short duration, with most examining outcomes over a year or less.
“Intermittent fasting isn’t a miracle cure but can be one approach among many for managing weight,” stated Dr. Luis Garegnani, who led the study and is the director of the Cochrane Associate Centre in Buenos Aires. “The results from fasting are likely similar to traditional dietary methods. It’s not evidently better, yet it’s not worse either.”
This method, where individuals restrict eating times or fast on select days, has surged in popularity, often touted for its potential benefits for weight loss, enhanced physical and mental health, and even anti-aging effects.
The Cochrane review conducted a thorough analysis using reliable techniques across randomized clinical trials that included nearly 2,000 adults from Europe, North America, China, Australia, and South America. These trials looked at various forms of intermittent fasting, including alternate-day fasting, the 5:2 diet, and time-restricted eating.
Aside from minimal weight loss benefits, the researchers did not find substantial evidence that intermittent fasting improves quality of life more than traditional diets.
Garegnani pointed out the need to clarify evidence around fasting due to its immense popularity and extensive media promotion. Many studies analyzed are short-term and lack quality, complicating solid conclusions about potential benefits. Interestingly, none of the 22 studies in the review gauged participants’ satisfaction with fasting.
Dr. Zhila Semnani-Azad from the National University of Singapore remarked that the potential benefits of intermittent fasting could be influenced by timing, given how the body’s circadian rhythms tie into metabolism. Research in animals suggests that fasting might modify fat usage, enhance insulin sensitivity—which is crucial for diabetes management—and reduce inflammation. She also mentioned that intermittent fasting could promote aging and longevity by initiating autophagy, the body’s recycling mechanism. However, the lack of a universal definition for intermittent fasting complicates understanding its full effects.
Professor Maik Pietzner, a health data modeling expert at the Berlin Institute of Health at Charité, expressed surprise at how minimal weight loss from fasting was compared to inactivity. Yet, he noted that this aligns with evidence that people tend to be less physically active while fasting, highlighting the challenges of losing weight without medications.
Moreover, the findings are consistent with his own research, indicating that brief fasting periods, even up to two days, have little impact on bodily changes. Notably, in one study he conducted where participants consumed only water for seven days, significant changes to their blood proteins didn’t manifest until after three days.
“If people feel good on these diets, I wouldn’t discourage them, but our work, along with others, clearly indicates that there’s no strong evidence for beneficial effects aside from perhaps moderate weight loss,” Pietzner noted. “Our bodies have adapted to periods of food scarcity and handle extended fasting well, but that doesn’t imply we perform better once these evolutionary traits kick in.”
