Intermittent fasting has become one of the most talked-about weight loss strategies in recent years, promoted by celebrities and wellness influencers alike. Stars like Jennifer Aniston, Terry Crews, and Kourtney Kardashian have publicly endorsed the practice, lending it a kind of pop-culture credibility that goes well beyond the scientific literature. The method typically involves eating only within a set window of time during the day, for example between 11 a.m. and 7 p.m., or following a pattern where five days of normal eating are followed by two days of drastically reduced calorie intake. Despite all the enthusiasm surrounding it, a major new analysis suggests that the results may not live up to the hype.
Researchers at the Cochrane Institute in the United Kingdom analyzed 22 separate studies involving 2,000 overweight or obese adults to assess how effective short-term intermittent fasting really is for losing weight. The goal was to determine whether the method worked better than standard dietary guidance or no guidance at all. Their findings revealed that people who practiced intermittent fasting over a 12-month period lost an average of about 3 percent of their body weight. That falls short of the 5 percent threshold that physicians generally consider to be a clinically meaningful reduction.
Luis Garegnani, a researcher from Universidad Hospital Italiano de Buenos Aires who led the study, expressed concern about how the method has been presented to the public. He stated that the excitement generated around fasting and its supposed effects on weight loss and overall health was “worrying.” “Intermittent fasting may be a reasonable option for some people, but current evidence does not justify the enthusiasm we see on social media,” he told BBC. One important factor that may explain the modest results is that people who fast within a time-restricted window do not necessarily consume fewer total calories overall, which researchers believe could be a key reason why the weight loss remains limited.
Eva Madrid, a senior author on the study, emphasized that weight loss is not a one-size-fits-all matter. “Doctors will need to approach each case individually when advising overweight adults on how to lose weight,” she noted. The researchers acknowledged they were “moderately confident” in their conclusions but also recognized that more research is needed, particularly regarding different fasting approaches and how they affect men and women differently, as well as people of varying body mass index levels and racial backgrounds. The study underscores that the biology of weight loss is far more complex than any single dietary trend can address.
Dr. Baptiste Leurent, an associate professor of medical statistics at University College London, offered a blunt assessment of the findings. He said the study provides “a clear indication that intermittent fasting offers modest benefits” and added that this is “another example of a disconnect between public perception and scientific evidence.” Professor Keith Frayn of the University of Oxford pushed back on the claims often made by fasting proponents that the practice produces “special effects on metabolism.” He pointed out that when it comes to losing weight, there are no “quick fixes” beyond simply reducing calorie intake, suggesting the metabolic benefits many people attribute to fasting may have little scientific grounding.
It is worth understanding what intermittent fasting actually is at a broader level. The term covers a variety of eating patterns, all of which involve cycling between periods of eating and periods of fasting or caloric restriction. The most well-known formats include the 16:8 method, where eating is limited to an 8-hour window each day, and the 5:2 approach, in which a person eats normally for five days and then restricts intake to around 500 to 600 calories on the remaining two days. Proponents have long argued that fasting triggers metabolic changes that go beyond simple calorie reduction, including shifts in insulin sensitivity and cellular repair processes. Obesity is generally defined as having a body mass index of 30 or higher, while overweight is classified as a BMI between 25 and 29.9. Clinically significant weight loss, meaning the kind associated with measurable improvements in health outcomes like reduced blood pressure or improved blood sugar control, is typically defined as losing 5 percent or more of total body weight. These benchmarks matter because they help separate treatments that make people feel like they are doing something from those that actually move the needle on long-term health.
Share your thoughts on intermittent fasting and whether this research changes your perspective in the comments.
