Intermittent fasting for weight loss: New study reveals limited benefits

A large review of 22 previous studies involving nearly 2,000 adults suggests that intermittent fasting may make little to no difference to weight loss and quality of life for people who are overweight or obese. While the practice could potentially improve some body functions, more evidence is needed. The review, published in the Cochrane Database of Systematic Reviews, found that intermittent fasting was not significantly better than standard dietary advice or no advice at all for weight loss.

Intermittent fasting, a popular approach to weight loss, involves fasting on some days of the week and eating normally on others, or restricting eating to a short window each day. Examples include the 5:2 diet and time-restricted eating. The research team examined studies with a duration of up to 12 months.

Compared to traditional dieting advice, such as reducing calorie intake and eating more healthily, intermittent fasting showed little to no difference in people's weight loss or quality of life. It also made little to no difference compared to those offered no advice or who were waiting for advice on weight loss. The effect on quality of life was not clear in these comparisons.

Researchers expressed moderate confidence in these findings but were less confident when comparing standard dieting and intermittent fasting. Many of the included studies did not use the most robust methods and involved small numbers of participants, making it difficult to determine the true effects.

Luis Garegnani, lead review author from the Universidad Hospital Italiano de Buenos Aires, voiced concern about the online enthusiasm for fasting.

"Intermittent fasting may be a reasonable option for some people, but the current evidence doesn't justify the enthusiasm we see on social media," he said.

However, the researchers acknowledged that individual responses vary and some people might benefit.

"Doctors will need to take a case-by-case approach when advising an overweight adult on losing weight," said senior review author Eva Madrid.

The review highlighted the need for more research into the impact of intermittent fasting on other health aspects. This includes its effect on type 2 diabetes, other underlying health conditions, and overall satisfaction. Further detail is also required on how different types of intermittent fasting might affect men and women separately, as well as individuals with different BMIs and from various countries. The studies included in the review were conducted in Europe, North America, China, Australia, and South America.

Dr. Baptiste Leurent, associate professor in medical statistics at University College London, stated that the individual studies collectively offer a clear indication of limited 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, commented on the widespread promotion of intermittent fasting for weight loss, often based on claims of special metabolic effects.

"This study shows that such claims can have little relevance," he said, emphasizing that there are no quick fixes for overweight or obese individuals beyond calorie reduction.

It is widely accepted that many people find intermittent fasting a useful method to avoid weight gain, although this was not directly investigated in the review. In the UK, approximately 1.6 million adults are thought to be using weight loss injections like Wegovy and Mounjaro, primarily through private prescriptions. A recent study indicated that individuals who discontinue these weight loss injections may regain weight up to four times faster than those who stop conventional dieting and exercising.