Intermittent fasting may not help people who are overweight or obese lose weight, a large review suggests.
The researchers say the popular practice of fasting on some days of the week and eating normally on others « may make little to no difference to weight loss and quality of life ».
But they say intermittent fasting could still improve overall health through helpful changes to some body functions, though more evidence is needed.
Examples of intermittent fasting include the 5:2 diet and restricting eating to a short window – often about eight hours – every day.
The research team looked at the results of 22 previous studies involving nearly 2,000 adults to find out if short-term intermittent fasting (over a period up to 12 months) was better at helping adults lose weight than standard dietary advice, or no advice at all.
Intermittent fasting is a fairly new approach to losing weight, and has gained popularity in recent years. Different types include:
Compared to giving people traditional advice on dieting, such as reducing calorie intake and eating more healthily, the review found intermittent fasting made little to no difference to people’s weight loss or quality of life.
Compared to those offered no advice or who were waiting for advice on weight loss, it also made little to no difference, although its affect on quality of life was not clear.
Although the researchers say they are « moderately confident » on the results for weight loss when comparing intermittent fasting with no advice, they are less confident about the other findings.
Most of the studies they looked at did not use the most robust methods and included small numbers of people, making it difficult to work out the true effects.
The review, published in the Cochrane Database of Systematic Reviews, says more research is needed to look at the impact of intermittent fasting on other aspects of people’s health, such as the status of their type 2 diabetes and other underlying health conditions, and how satisfied it made them feel.
There are also many different types of intermittent fasting and more detail is needed on how they could impact men and women separately, in addition to those with different BMIs and from different countries.
The studies in this review took place in Europe, North America, China, Australia and South America.
Dr Baptiste Leurent, associate professor in medical statistics at University College London said, taken together, the individual studies « provide a clear indication that intermittent fasting offers little benefit ».
« This is yet another example of a misalignment between public perception and the scientific evidence, » he added.
Prof Keith Frayn, emeritus professor of human metabolism at the University of Oxford, said intermittent fasting had been widely promoted as a means of achieving weight loss – often on the basis of claims it had « special effects on metabolism ».
« This study shows that such claims can have little relevance, » he said, adding that there were no « quick fixes » for those who are overweight or obese beyond reducing calorie intake.
It is widely accepted that many people find intermittent fasting a good way to avoid putting on weight, although this wasn’t researched in the review.
Around 1.6 million adults in the UK are thought to be using injections such as Wegovy and Mounjaro to lose weight – mostly bought through private prescriptions rather than on the NHS.
A recent study found people who stop using the weight loss jabs can put weight back on four times faster than those who stop conventional dieting and exercising.
