Trendy diet loved by millions has no benefit for weight loss compared to traditional advice, study finds
It’s a diet trend embraced by Hollywood A-listers and millions of people watching their weight.
But intermittent fasting may not actually help you lose weight, according to the most comprehensive review of the evidence to date.
Scientists from the Cochrane Institute, the ‘gold standard’ for evidence-based medicine, analyzed data from 22 studies involving 2,000 adults, most of whom were obese or overweight, who followed either the fashionable plan or traditional dieting methods such as calorie restriction.
They found that eating for just a few hours every day did not lead to more weight loss compared to standard dieting methods, or even to doing nothing at all.
Overall, within 12 months, intermittent fasters lost about three percent of their body weight, below the five percent threshold that doctors consider to be clinically meaningful.
It’s unclear why intermittent fasting did not cause more weight loss than other diet plans, but researchers have previously suggested this could be because those on the diet still eat the same number of calories as others or exercise less.
Supporters claim the diet helps to burn fat, triggers weight loss, boosts energy and even extends their lifespan.
But in recent years, doctors have begun to raise concerns over the diet after studies linked it to a higher risk of colon cancer and type 2 diabetes.
Jennifer Aniston previously said that she uses intermittent fasting, saying in 2019 that she only drinks water in the mornings or delays her first meal until midday
Dr Luis Garegnani, a researcher at Universidad Hospital Italiano de Buenos Aires, who led the review, said: ‘Intermittent fasting just doesn’t seem to work for overweight or obese adults trying to lose weight.’
Intermittent fasting involves a person limiting their caloric intake to either certain hours of the day or days of the week, to lose weight and control eating habits.
Popular iterations include the 14:10 plan — where a person only eats within a 10-hour window — and the 5:2 — where someone eats five days a week and fasts for two.
There has been a health halo around intermittent fasting since it took off in the 2010s after celebrities such as Jennifer Aniston and Mark Wahlberg revealed they swore by the plan. Today, an estimated one in 10 Americans follows the diet.
Aniston revealed she was a fan of the diet in 2019, saying she drinks only water in the mornings and delays her first meal until midday.
Wahlberg, who is famous for his strict lifestyle regimen, has claimed he confines his eating to between 12pm and 6pm.
Mark Wahlberg, shown above in 2019 near Bridgetown, Barbados, has also previously said he swears by intermittent fasting
The findings come as 40 percent of Americans are obese or overweight, federal suggests.
Worldwide adult obesity has also more than tripled since 1975, according to the World Health Organization. In 2022, 2.5 billion adults were overweight. Of these, 890 million were living with obesity.
In their review, scientists at the Cochrane Institute searched databases for studies that compared participants who did intermittent fasting and other diet methods.
The trial involved 1,995 adults from Europe, North America, China, Australia and South America. It examined different kinds of intermittent fasting, including the 5:2 diet, where people fast for two days a week.
Other diets include eating in a calorie deficit, when someone consumes fewer calories than they burn in a day, and a low-carb diet.
The review only included 22 studies, which researchers said was because many studies into intermittent fasting are short-term and of poor quality.
They said this made it difficult to reach firm conclusions about the possible benefits of the diet plan.
Overall, people who followed intermittent fasting lost about 0.33 percent more of their body weight than those who followed standard dieting methods. Compared to those who took no action to reduce their weight, people who followed intermittent fasting lost 3.42 percent more of their body weight on average.
Intermittent fasting does not lead to more weight loss than traditional diet methods, researchers have concluded (stock image)
This was not statistically significant, however, which researchers said showed that intermittent fasting was no better for weight loss than standard diets.
Researchers said the results had low certainty, however, which they said was due to the limitations of the data used.
The study had only a small sample size that spanned a very large georgraphical area. Researchers said they needed more and much larger studies to confirm the results.
Dr Eva Madrid, a researcher at Cochrane Evidence Synthesis Unit Iberoamerica and senior author on the study, said: ‘With the current evidence available, it’s hard to make a general recommendation.
‘Doctors will need to take a case-by-case approach when advising an overweight adult on losing weight.’
Their research follows a separate paper led by Harvard scientists, published in June 2025, that reviewed 99 studies but also found intermittent fasting was no better than regular dieting.
The team of international researchers concluded that the benefits from fasting were essentially ‘trivial’ compared to standard diet plans.
Neither eating meals in a specific time window, like in an eight-hour period, nor doing fasting for five days of the week and then eating normally for two were found to be any better for losing weight.
In fact, alternate-day fasting, where people fast for 24 hours on alternate days, was only found to help people lose more weight, with dieters slimming down 2.84lbs (1.29kg) more, on average.
However, this difference didn’t meet what the researchers said was the minimum clinical threshold of 4.4lbs (2kg).
In the study, researchers analyzed the results of 99 randomised clinical trials involving 6,582 adults, aged 45 on average, to compare intermittent fasting with calorie-cutting diets.
Writing in the British Medical Journal, which published the findings, the scientists said that while their data suggested that intermittent fasting was better for losing weight than not dieting at all, it didn’t stand out compared to basic calorie counting.
‘Minor differences were noted between some intermittent fasting diets and continuous energy restriction, with some benefit for an alternate day fasting strategy with weight loss in shorter duration trials,’ they added.
‘All intermittent fasting strategies and continuous energy restriction diets showed a reduction in body weight when compared with an ad-libitum diet (allowing yourself to eat at any time).
‘Of three intermittent fasting diets, alternate day fasting showed benefit in body weight reduction compared with continuous energy restriction.’
