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An international study has found that intermittent fasting has little to no benefit for overweight or obese adults, but an Australian researcher has raised questions about limitations of the review.
A report from the Cochrane review found that the results of intermittent fasting are so poor compared to other weight loss methods that obese adults are better off following traditional dietary advice, or doing nothing at all.
International researchers analysed evidence from 22 randomised clinical trials of almost 2000 adults, including some from Australia, investigating data on a range of intermittent fasting methods, including alternate-day fasting, periodic fasting, and time-restricted feeding.
They found that intermittent fasting did not appear to have a clinically meaningful effect on weight loss.
Adelaide University Group Leader of Obesity and Metabolism Professor Leonie Heilbronn says the Cochrane review findings were similar to dozens of similar meta-analyses of this topic — that intermittent fasting produces similar weight loss to other moderate calorie restriction interventions of around 7% after 6-12 months, with far better weight loss results for other weight loss methods such as very low calorie diet (10-15%), pharmacotherapy (15-20%) or surgery (>20%).
However, she says a limitation of this latest study is that it should not have incorporated different types of intermittent fasting into the one review and did not consider wider health benefits beyond weight loss.
“This review combines many forms of intermittent fasting, which is a mistake,” Professor Heilbronn says.
“There are many types of ‘intermittent fasting’, and they are not equivalent for weight loss and should not be mashed together.”
“There is some evidence that health is improved despite modest weight loss by time-restricted eating due to better alignment of circadian rhythms.”
Professor Heilbronn says the review also included very few studies to come to its conclusions.
“Type of control matters. Some of the control groups were not completely inactive or waitlist — they received some information and guidance for weight loss. This reduces the apparent difference between intermittent fasting and control,” she says.
“They have heterogeneous results because they are lumping together diets that should not be put together. Which will result in heterogeneity … some also include those with diabetes who are typically refractory to weight loss (even with semaglutide).”
Professor Heilbronn says GP’s can be confident recommending intermittent fasting as a proven alternative to continuous calorie restriction over 6-12 months, based on the available scientific evidence.
“Many people find it very difficult to keep weight off beyond 12 months, no matter what approach they use,” she says.
“This is because the body has biological mechanisms that encourage weight regain after weight loss.”
“For example, levels of satiety peptides and other hormones that make you feel full drop, leptin also drops, decreasing your energy expenditure, and hunger hormones like ghrelin increase.”
“As a result, weight often returns after a year, whether someone followed a calorie-restricted diet or intermittent fasting.”
“Exercise and weight loss medications can help maintain the loss by counteracting these biological signals.”
Nance Haxton was a journalist at the ABC for nearly 20 years. She’s also worked as an Advocate at the Disability Royal Commission helping people with disabilities tell their stories and as a senior reporter for the National Indigenous Radio Service.
In that time she’s won a range of Australian and international honours, including two Walkley Awards, and three New York Festivals Radio Awards trophies.
Now freelancing as The Wandering Journo, Nance is independently producing podcasts including her personal audio slice of Australia “Streets of Your Town”.
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