Experts debate intermittent fasting for obesity weight loss

A study suggests intermittent fasting is unlikely to lead to weight loss in obese and overweight adults. The researchers compared intermittent fasting to following traditional dietary advice and making no changes. It did not appear to have a clinical effect on weight loss in either comparison, a finding that multiple experts disagree on. 

Intermittent fasting has gained popularity in recent years for its metabolic benefits and rapid weight loss, driven by social media influencers.

The study’s findings have sparked debate, with several experts offering differing opinions. While some praise the study for its conductability and accuracy, others claim it to be vague and misleading.

“While this review is of interest and will generate clicks, it should not distract from the consensus from other studies in the scientific literature that intermittent fasting regimens are an effective tool for weight loss,” comments Adam Collins, associate professor of nutrition at the University of Surrey, UK. Collins was not involved in the research. 

“This robust review and meta-analysis of intermittent fasting focuses specifically on weight loss and quality-of-life benefits. The headline finding that intermittent fasting is no better (or worse) than standard dietary advice or doing nothing is attention-grabbing, but should be interpreted with a little caution.”

Evidence doesn’t justify

The review, published in the Cochrane Database of Systematic Reviews, included 22 studies with data from 1,995 participants. The studies were conducted in North America, Australia, China, Denmark, Germany, Norway, and Brazil, published between 2016 and 2024. Most of them observed the participants for 12 months.

It looked at various forms of fasting, including alternate-day fasting, periodic fasting, and time-restricted fasting.

When comparing intermittent fasting to no intervention and traditional dietary advice, the study did not show a significant effect on weight loss.When comparing intermittent fasting to no intervention and traditional dietary advice, it did not show a significant effect on weight loss.

“Intermittent fasting just doesn’t seem to work for overweight or obese adults trying to lose weight,” says Luis Garegnani, lead author of the review from the Universidad Hospital Italiano de Buenos Aires Cochrane Associate Centre, Argentina.

“It may be a reasonable option for some people, but the current evidence doesn’t justify the enthusiasm we see on social media.”

He also adds that obesity is a chronic condition; therefore, short-term trials (up to 12 months) make it difficult to guide long-term solutions. 

The study’s researchers note that reporting side effects was inconsistent across trials, making it difficult to draw conclusions. They say the findings should therefore “serve as clues rather than be extrapolated to the entire population, as they may vary depending on sex, age, ethnic origin, disease status, or underlying eating disorders or behaviors.”

Creating debate

Dr. Baptiste Leurent, an associate professor in Medical Statistics at the UCL Department of Statistical Science, UK, says the paper appears to be “very well conducted.” He refers to Cochrane reviews as “the gold standard” for reviewing the available evidence on health interventions.

“This review found absolutely no benefit of intermittent fasting on weight loss, when compared to standard dietary advice. When compared to not doing anything, however, it did identify a small benefit, with a 2–5% average reduction in weight six to 12 months later. This was statistically significant but remains small.”

However, Collins notes: “What is more intriguing is their conclusion that intermittent fasting shows no greater weight loss than ‘doing nothing.’ This is, again, a little misleading.”

“The resultant box plot does imply that weight loss is more favorable in the intermittent fasting group, as you would expect. This appears to be at odds with the statement of results in the text.”

He adds that there are two possible explanations for the unclear differences in weight loss outcomes. Firstly, the studies may not be representative of typical intermittent fasting, such as fasting a few times a week rather than every day.

Secondly, Collins points to potential bias among the participants, such as the tendency of subjects to change their behavior when aware of being part of a study. Therefore, it could be that people in the control group lose weight or make dietary changes as they are being monitored about their habits.

Contradicting research

In previous studies, the findings of intermittent fasting and its benefits and harms contradict as well.

Collins says the conclusion that intermittent fasting shows no greater weight loss than doing nothing is a bit misleading.Similar to the new study, previous research from Shanghai, China, was also met with skepticism. It found that when following an intermittent fasting eating schedule, participants had a 91% higher risk of death from cardiovascular disease compared to those eating across the standard 12 to 16 hours per day.

The Shanghai study was met with criticism from over 30 researchers, who outlined research errors and questioned its validity.

Meanwhile, researchers at Columbia University in the US suggested that intermittent fasting offers similar benefits to conventional calorie-restricted weight-loss diets and demonstrates “greater benefits” than cutting calories and other fasting approaches.

Other previous research linked the metabolic and cardiovascular improvements from intermittent fasting to its effect of reducing calorie intake, even if unintended, rather than restricting the timing of eating.

The authors from the new study conclude that further research is needed to address the effect of intermittent fasting on several outcomes, including participant satisfaction, diabetes status, and overall measures of comorbidities.

“These studies must consider different populations where obesity and overweight have different burdens, like those from low‐ and middle‐income countries and high‐income countries, men or women separately, and different body mass index categories.”