An international study has found that intermittent fasting has no benefit for overweight or obese adults, but an Australian researcher has raised questions about the review’s limitations.
A Cochrane review report found that the results of intermittent fasting are worse than other weight loss methods in obese adults who are better off following conventional diet advice, or doing nothing at all.
International researchers analyzed evidence from 22 randomized clinical trials of nearly 2,000 adults, some from Australia, examining data on intermittent fasting methods, including alternate-day fasting, intermittent fasting, and time-restricted eating.
They found that intermittent fasting did not have a clinically meaningful effect on weight loss.
Professor Leonie Heilbron, head of the Obesity and Metabolism Group at the University of Adelaide, said the findings of the Cochrane review were similar to dozens of similar meta-analyses on the subject – that intermittent fasting after 6-12 months resulted in a weight loss of around 7% similar to that of very low weight loss methods. (10-15%), pharmacotherapy (15-20%) or surgery (>20%).
However, he says a limitation of this latest study is that it didn’t include different types of intermittent fasting in one review and didn’t consider the broader health benefits beyond weight loss.
“This review lumps many types of intermittent fasting together, which is a mistake,” says Professor Heilbron.
There are many types of ‘intermittent fasting’, and they are not equivalent to weight loss and should not be mixed together.”
“There is some evidence that time-restricted eating improves health despite weight loss due to better alignment of circadian rhythms.”
Professor Heilbron says the review included too few studies to reach this conclusion.
“The controls sort of matter. Some of the control groups weren’t completely inactive or on a waiting list—they got some information and instructions to lose weight. That reduces the apparent difference between intermittent fasting and controls,” he says.
“They have contradictory results because they combine diets that should not be combined. “Which would lead to heterogeneity… some include people with diabetes that usually prevents weight loss (even with semaglutide).”
Professor Heilbron says, based on the available scientific evidence, GPs can confidently recommend intermittent fasting as a proven alternative to continuous calorie restriction over 6-12 months.
“Most people have a hard time keeping the weight off after 12 months, no matter what method they use,” she says.
“This is because the body has biological mechanisms that encourage weight regain after weight loss.”
“For example, levels of peptides and other hormones that make you feel full decrease, leptin also decreases, your energy expenditure decreases, and hunger hormones such as ghrelin increase.”
“As a result, the weight is often regained after a year, if one follows a calorie-restricted diet or intermittent fasting.”
“Exercise and weight loss medications can help prevent damage against these biological markers.”
Nance Haxton was a journalist at the ABC for almost 20 years. She has also worked as an advocate at the Disability Royal Commission helping disabled people tell their stories and as a senior reporter for the National Indigenous Radio Service.
During this time she won a series of Australian and international honours, including two Walkley Awards, and three New York Festival Radio Award trophies.
Now freelancing as Wandering Journo, Nance independently produces podcasts including her own Australian audio piece “Streets of Your City”.
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