Intermittent fasting probably doesn’t help with weight loss

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

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

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

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

First, they compared intermittent fasting to traditional dietary advice and found that there was likely no significant difference in weight loss. Then they compared intermittent fasting to doing nothing at all and found that it probably didn’t lead to additional weight loss either. “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 between trials make it difficult to draw definitive conclusions, he says. Yet when researchers grouped the results by gender or type of intermittent fasting, they found that this approach still didn’t seem to help with weight loss.

But Satchidananda Panda of 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 completed the intervention, what exactly are we systematically looking at? he said. “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 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 people, but it should not distract from broader population-wide strategies to prevent and manage obesity.