Has science proven any benefits for intermittent fasting?

Yes, but those benefits are limited.

First, for the uninitiated: Intermittent fasting diets restrict a person’s caloric intake during certain hours or days. For instance, a person might follow a 16:8 fasting diet, eating only in an 8-hour window each day and fasting for the remaining 16 hours. Some diets are more extreme—dieters might drastically reduce their intake to about 500-600 calories for several days per week then eat normally for the other days.

Proponents of intermittent fasting often claim the practice can dramatically lower insulin levels, reduce cancer risks, and even extend cell life. However, current science doesn’t support those types of conclusions.

“Many diet and exercise trends have origins in legitimate science, though the facts tend to get distorted by the time they achieve mainstream popularity. Benefits are exaggerated,” Roger Collier wrote in the Canadian Medical Association Journal. “Risks are downplayed. Science takes a back seat to marketing.”

Collier noted that intermittent fasting might encourage unhealthy practices such as binge-eating; people finish their fasts, then eat large amounts of junk food. That approach can be dangerous.

In November 2018, researchers at the German Cancer Research Center published one of the largest investigations on intermittent fasting to date. They compared intermittent fasting to conventional caloric restriction diets. The group that followed an intermittent fasting plan lost weight—but so did the conventional diet group.

"In participants of both groups, body weight and, along with it, visceral fat, or unhealthy belly fat, were lost and extra fat in the liver reduced,” Ruth Schübel, a scientist at the center, said.

In other words, researchers found no substantial difference between the two groups. Still, they noted that intermittent fasting can be a safe and effective method of weight loss.

"... for some people it seems to be easier to be very disciplined on two days instead of counting calories and limiting food every day," noted Tilman Kühn, the trial’s leading scientist. "But in order to keep the new body weight, people must also permanently switch to a balanced diet following [German Nutrition Society] recommendations."

What about the other benefits of intermittent fasting? While the practice has shown promising results in animal research, those benefits could be attributed to the overall weight loss and caloric deficit of the diet strategy. In other words, any other diet would likely produce the same types of results.

The takeaways: Don't assume that fasting will work better than any other structured diet, don't use fasting as an excuse to binge on low-quality foods, and most importantly, if you're going to try an intermittent fasting plan, you should review it with a physician or dietitian first.