Intermittent fasting probably doesn’t help with weight loss

Intermittent fasting appears to be no more effective for weight loss than doing nothing at all, according to a review of studies involving people who were overweight or had obesity.

The diet has become a popular weight-loss strategy in recent years and involves alternating between periods of fasting and normal eating. This can include eating only during a set window each day, such as the 16:8 diet, where you fast for 16 hours and eat within an 8-hour period; or eating normally on some days and very little on others, like the 5:2 diet, where you eat as normal on five days a week and restrict calories on the other two.

The idea is that limiting when people can eat reduces their overall calorie intake, but one randomised-controlled trial found it is no better for weight loss than calorie counting.

To learn more, Luis Garegnani at the Italian Hospital of Buenos Aires in Argentina and his colleagues analysed data from 22 randomised-controlled studies of intermittent fasting, involving nearly 2000 adults across North America, Europe, China, Australia and South America. The participants were aged 18 to 80 and were either overweight or had obesity.

First, they compared intermittent fasting to traditional dietary advice and found there is probably no significant difference in terms of weight loss. Then they compared intermittent fasting to doing nothing at all and found that it also probably doesn’t lead to more weight loss. “Intermittent fasting just doesn’t seem to work for overweight or obese adults trying to lose weight,” Garegnani said in a press release.

However, inconsistencies across the trials make it challenging to draw firm conclusions, he says. Still, when the researchers grouped the results by gender or type of intermittent fasting, they found the approach still didn’t seem to help with weight loss.

But Satchidananda Panda at the Salk Institute for Biological Studies in California notes that most of the studies in the review didn’t measure adherence to intermittent fasting. “If we don’t know whether participants actually followed the intervention, what, exactly, are we systematically reviewing?” he says. “It’s a bit like building a cathedral on quicksand and then performing a meta-analysis of the architecture.”

The analysis focused on weight loss, so it also isn’t clear if intermittent fasting has other health effects, good or bad. For instance, some studies suggest it may increase the risk of heart disease, while others indicate it boosts immunity and improves gut and liver function.

“Intermittent fasting is not a miracle solution,” says Garegnani. “[It] may be a useful option for some individuals, but it shouldn’t distract from broader, population-level strategies to prevent and manage obesity.”