News about intermittent fasting seems to change as frequently as the apps on your phone need upgrading. Yet another new study about the eating practice seeks to put doubts to rest after rounding up data from 22 randomized clinical trials.
Intermittent fasting (IF) is a diet in which calories are only consumed during specific windows of time each day or week. The practice first began cycling through news headlines in the early 2010s, largely thanks to a BBC documentary called Eat, Fast and Live Longer hosted by British journalist Michael Mosley. Mosley practiced the 5:2 diet, which involves eating normally five days a week, and severely restricting calories on the other two days. After the success of that program, fitness influencers got a hold of the practice a few years later, adding a 16:8 spin to it, which proposes eating during an eight-hour period each day and fasting for the other 16.
Over the years, there have been various studies examining the trend, many reaching different conclusions. Now, a new meta-analysis by researchers working with Cochrane says that – at least in terms of weight loss – IF is no better than following standard dietary advice. The analysis defined standard dietary advice as "reducing calories and changing eating habits to eat healthier foods or different amounts of protein, carbohydrate and fat.” Even though the study did find a modest improvement over no diet at all, with a 2-5% reduction in weight 6-12 months later, the researchers say it isn't clinically meaningful.
"Intermittent fasting just doesn’t seem to work for overweight or obese adults trying to lose weight," said first study author Luis Garegnani from Universidad Hospital Italiano de Buenos Aires Cochrane Associate Centre. "It may be a reasonable option for some people, but the current evidence doesn’t justify the enthusiasm we see on social media."
The 22 trials the team looked at involved 1,995 adults living in North America, Australia, South America, China, and Europe, and included multiple types of intermittent fasting including alternate-day, periodic, and time-restricted eating.
Beyond weight loss
The findings back up previous research showing little weight loss benefits to intermittent fasting, such as one that showed the 16:8 style of intermittent fasting was statistically no better than generally restricting calories but eating all day. However, there may be benefits to IF that go beyond weight loss, according to other studies. For example, a 2023 study showed that restricting food intake to a six-hour window improved the sleep patterns of mice and helped them perform better on memory and other cognitive tests. A human study from the same year showed that the 16:8 diet led to better long-term blood sugar levels in type 2 diabetics.
In fact, according to Adam Collins, associate professor of nutrition at the University of Surrey, the study " should not distract from the consensus from other studies in the scientific literature that IF regimens are an effective tool for weight loss. They can also be practically advantageous for many people."
Surrey was not involved in this research, but has carried out his own research into time-restricted eating.
He adds that "several studies (including our own) have suggested IF regimens may offer other metabolic benefits that are independent of weight loss, which is where much of the research on these regimens is now focused. This makes these approaches more universally useful, not just for those who are overweight or living with obesity – for example, in the management of metabolic disease, and the maintenance of weight once it is lost (e.g. post-GLP-1).”
So, in the end, the debate over intermittent fasting is likely to continue but remain more focused on its potential metabolic benefits rather than its ability to provide better weight loss benefits than any other diet.
Source: Cochrane
