Intermittent fasting probably doesn’t help with weight loss

According to a review of studies involving overweight or obese people, intermittent fasting appears to be no more effective for weight loss than doing nothing at all.

Dieting has become a popular weight loss strategy in recent years and involves alternating 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 8 hours; or eating normally on some days and very little on others, such as the 5:2 diet, where you eat as usual five days a week and cut calories the other two.

The idea is that restricting when people can eat reduces their overall calorie intake, but one randomized controlled trial found that it’s no better for weight loss than counting calories.

To learn more, Luis Garegnani at the Italian Hospital in Buenos Aires, Argentina, and colleagues analyzed data from 22 randomized controlled trials of intermittent fasting involving nearly 2,000 adults in North America, Europe, China, Australia and South America. Participants were between the ages of 18 and 80 and were overweight or obese.

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

However, test inconsistencies make it difficult to draw firm conclusions, he says. Yet when the researchers grouped the results by gender or type of intermittent fasting, they found that the approach still didn’t 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 did not measure adherence to intermittent fasting. “If we don’t know whether participants actually adhered to the intervention, what exactly are we systematically checking for?” he says. “It’s a bit like building a cathedral on quicksand and then doing a meta-analysis of the architecture.”

The analysis focused on weight loss, so it’s also unclear whether intermittent fasting has other health effects, good or bad. For example, some studies suggest it may increase the risk of heart disease, while others suggest it boosts immunity and improves bowel and liver function.

“Intermittent fasting is not a magic bullet,” says Garegnani. “[It] may be a useful option for some individuals, but should not distract from broader population-level strategies to prevent and manage obesity.”

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