Intermittent fasting has surged in popularity thanks to wellness influencers, social media and celebrity fans such as Jennifer Anniston, Jimmy Kimmel and Hugh Jackman.

But now, new research claims the “hype outpaces the evidence” when it comes to the effectiveness of this widespread trend compared to other types of diets.

“Intermittent fasting just doesn’t seem to work for overweight or obese adults trying to lose weight,” said Luis Garegnani, lead author of the review from Argentina’s Cochrane Associate Centre.

Garegnani warned that while restricting eating in this way may be “a reasonable option” for some people, “the current evidence doesn’t justify the enthusiasm we see on social media”.

The researchers analysed evidence from 22 randomised clinical trials involving almost 2000 adults across North America, Europe, China, Australia, and South America.

The trials examined multiple forms of intermittent fasting such as alternate-day and periodic fasting (including the 5:2 diet popularised by British TV personality and author Dr Michael Mosley, which involves five days of eating and two days of fasting), and the 16:8 diet (involving a 16-hour fasting period followed by an eight-hour eating window).

Australian actor Jackman reportedly followed the 16:8 diet to help attain his impressive Wolverine physique, while Friends star Anniston, singer Moby, and actor Vanessa Hudgens have also spoken about being fans of this method.

Kimmel, meanwhile, was an early proponent of whole-day fasting, writing in The Men’s Journal in 2017: “People call it the 5:2 diet, but I’ve been doing it since before it had a name. On Monday and Thursday, I eat fewer than 500 calories a day, then I eat like a pig for the other five days.”

Despite such celebrity endorsements, the Cochrane researchers said their analysis found intermittent fasting did not appear to have a “clinically meaningful effect” on weight loss compared to standard dietary advice or even “doing nothing”.

They acknowledged that evidence was still limited, with many of the trials assessed involving small sample sizes and inconsistent reporting. In addition, few trials looked at the long-term results of intermittent fasting.

“With the current evidence available, it’s hard to make a general recommendation,” said Eva Madrid, a senior author with Cochrane. “Doctors will need to take a case-by-case approach when advising an overweight adult on losing weight.”

The late Michael Mosley was a key proponent of the 5:2 diet. Source: AAP

Obesity is a leading cause of death in high-income countries, with the number of obese adults worldwide more than tripling since 1975. In 2022-23, 65.8 per cent of adult Australians were overweight or obese, according to the Australian Bureau of Statistics.

But while the research may dishearten some of those who are seeking to lose weight, expert opinions more broadly suggest intermittent fasting should perhaps not be dismissed completely.

Professor Leonie Heilbronn, group leader of obesity and metabolism at Adelaide University, claimed the Cochran researchers made a mistake by mashing together different forms of intermittent fasting, stressing that they are not equivalent for weight loss.

Heilbronn described time-restricted eating as a milder intervention that resulted in two to three kilograms of weight loss over six to 12 months.

“There is some evidence that health is improved despite modest weight loss by time-restricted eating due to better alignment of circadian rhythms (but the jury is out – more trials required),” she wrote in a response on the Science Media Centre.

Heilbronn said intermittent or alternate-day fasting involved a 75-100 per cent energy restriction for two or three days a week and regular eating practice on other days.

“Most of the trials comparing calorie restriction against intermittent fasting have around 5 to 7 per cent weight loss in both groups and similar improvements in body weight and in diabetes and cardiovascular disease risk factors.”

Heilbronn also pointed out that the part of the Cochran review that compared intermittent fasting with “doing nothing” drew on only six previous studies, two of which involved time-restricted eating.

She concluded that intermittent fasting was a “proven alternative” to continuous calorie restriction over six to 12 months – but warned that many people find it very difficult to keep weight off beyond a year, no matter what approach they use.

“This is because the body has biological mechanisms that encourage weight regain after weight loss.”

Other doctors and researchers also point out that the promised benefits of intermittent fasting can extend beyond weight loss.

Jack Mosley ­– son of Michael Mosley, who died while out walking during a holiday on the Greek island of Symi in 2024 – has responded to the study by defending intermittent fasting.

In an article published in The Times in the UK, the GP and author said there was a lot of conflicting research about the 5:2 diet popularised by his father, with another meta-analysis conducted last year finding it significantly reduced body weight, body mass index, waist circumference, body fat percentage and a range of cardiovascular markers.

Jack Mosley also pointed out that Michael, whose bestselling books included The Fast Diet and The Fast 800, followed the diet to reverse his own type-2 diabetes and lose weight.

He said some people found intermittent fasting easier than continuous calories restriction, because they didn’t have to constantly think about what they were eating.

“My belief is that with any diet – whether the 5:2, or a traditional method of continuous energy restriction – the best is the one that suits you,” he wrote.

“Fasting is not for everyone. But both intermittent fasting and continuous calorie restriction are effective and valid routes to losing weight.”

Australian website Health Direct recommends that anyone considering intermittent fasting should speak to their doctor before they begin.