Key topics
- Intermittent fasting limits food intake to specific time windows for weight loss.
- Mixed results on weight loss, but some studies suggest it improves metabolism.
- Potential health benefits, including increased lifespan and improved metabolic health.
Sign up for your early morning brew of the BizNews Insider to keep you up to speed with the content that matters. The newsletter will land in your inbox at 5:30am weekdays. Register here.
Support South Africa’s bastion of independent journalism, offering balanced insights on investments, business, and the political economy, by joining BizNews Premium. Register here.
If you prefer WhatsApp for updates, sign up to the BizNews channel here.
From The Economist, published under licence. The original article can be found on www.economist.com
© 2025 The Economist Newspaper Limited. All rights reserved.
The Economist ___STEADY_PAYWALL___
It does for weight loss. Its other supposed benefits are debatable.
Diets come and diets go. One of the most popular today is “intermittent fasting” in which, as the name suggests, the idea is to limit one’s food intake to certain time windows. One popular variant, the “5-2 diet”, requires people to eat either very small amounts, or nothing at all, on two days a week, but imposes no restrictions on the other five.
Intermittent fasting is popular. And as a weight-loss strategy, it has several things going for it. One is that it is uncomplicated. There is no need to weigh the ingredients of every meal, as some diets demand, nor to change what you eat drastically. Limiting the restrictions to a couple of days a week, or several hours a day (most of which are spent asleep) also requires less willpower, which might make it easier to stick with.
Working out whether that actually translates into greater weight loss than other diets is difficult. Most studies find limited data and mixed results. The general consensus, says Nichola Ludlam-Raine, a dietitian and spokeswoman for the British Dietetic Association, is that intermittent fasting seems to work roughly as well for weight loss as traditional calorie-counting does.
Other health benefits might also beckon. Forcing lab animals to fast (albeit not intermittently) can increase their lifespans by up to 40%. It also appears to mitigate the physical decline that comes with old age, boost various markers of metabolic health and even reduce susceptibility to cancer.
Exactly how it does all that is not entirely clear. One important factor seems to be autophagy, the process by which cells break down and recycle parts of themselves. Cells become much keener on autophagy when nutrients are scarce. At the same time, autophagy seems to have a preference for attacking damaged and degraded parts of cells—and the accumulation of such cellular detritus is one of several mechanisms thought to underlie the decrepitude that comes with ageing.
The hope is that intermittent fasting might provoke a similar response in humans. There are theoretical reasons to think it might: the cellular mechanisms triggered by food shortages seem to have been conserved by evolution in all sorts of different animals. But running definitive human trials of the sort done on lab animals is impossible. “When we say ‘calorie restriction’ we mean nearly starving [the animals],” says Adam Collins, a nutrition researcher at the University of Surrey.
That leaves scientists reliant, for now, on smallish, short-lived studies that use less drastic diets and which rely on proxy measures of health such as insulin response or cholesterol levels. Their results are mixed. Dr Collins’s team, for instance, has published a randomised-control trial (the most rigorous sort) suggesting that intermittent fasting improves the metabolism of fats more than ordinary dieting does. A review paper published in April 2024 looked at 23 other studies and concluded that intermittent fasting was slightly better than ordinary dieting for overweight people when it came to improving levels of cholesterol and insulin. A similar article, published in January, found no meaningful difference for either weight loss or cardiovascular health.
There are also risks. A study in mice published in Nature in October 2024 found that severe fasting (where calories were cut by 40%) had downsides, including muscle mass loss and, possibly, weakened immune systems. Moderation, too, should be taken in moderation.
Read also:
