Intermittent fasting can help people lose weight and keep that weight off over the course of a year roughly as effectively as counting calories, according to a new study published in the Annals of Internal Medicine.

Study details

For the study, researchers took 77 participants with obesity — meaning they had a body mass index over 30 — and randomly placed them in one of three groups.

The first group could only eat between noon and 8 p.m. every day, the second group had to count calories and reduce daily energy intake by 25%, and the third group made no changes to their eating.

After six months, participants had a "weight management phase" in which the eating window for the intermittent fasting group was increased from eight to 10 hours and the calorie counting group had their caloric intake increased.

According to Krista Varady, a professor of nutrition at the University of Illinois Chicago and lead author on the study, this phase was implemented because "most people with diets will lose weight for about six months and after that it usually plateaus."

Throughout the 12-month course of the study, both weight loss groups had regular counseling with dieticians to advise them on healthy food choices and provide them with cognitive behavioral strategies to prevent weight gain.

At the end of the study, researchers found that those in the intermittent fasting group lost around 10 pounds more on average than those in the control group. Meanwhile, those in the calorie counting group lost around 12 pounds more. The difference between the two groups was not statistically significant.

The study also found that, while those in the intermittent fasting group were not told to watch their calories, they still reduced their daily caloric intake by around 400 calories.

Discussion

Some experts said the study results are encouraging because they show people can continue intermittent fasting for an extended period of time.

"That is pretty exciting," said Courtney Peterson, a professor of nutrition at the University of Alabama at Birmingham, who was not involved in the study. "This study has the most compelling results suggesting that people can stick with it, that it's not a fad diet in the sense that people can do it for three months and they fall off the wagon for a year."

Peterson noted that placing limits on when you can eat can have an "anti-snacking effect" that can help avoid mindless eating late at night. She added that data from her lab has also shown intermittent fasting can affect hormones and help to regulate appetite.

According to Varady, the study results suggest that intermittent fasting can lead to a kind of "natural calorie restriction," potentially because people have less time to eat.

"People usually eat within a 12-to-14-hour window, so all we're doing is cutting out around six hours," she said. "Mainly we're cutting out, I think, after-dinner snacks."

However, Adam Gilden, an associate professor of medicine at the University of Colorado who authored an accompanying editorial, noted the "intensive support" participants received from dieticians is significant.

"Most people who are doing this are not doing it with any type of dietary or behavioral support," he said. "They're doing it on their own."

Because of this, Gilden said many of his patients are not successful with intermittent fasting. He added that he's skeptical the technique would produce the same results in the real world without any support.

"There's nothing sort of magical about, 'I'm only going to eat for these eight hours per day,'" Gilden said. "The person doing that strategy still has to pay attention to what types of foods they're eating and the portions and the amounts."

However, Varady noted that calorie-counting can be more labor-intensive than intermittent fasting, which can make it difficult to stick with.

"What we're showing is that people don't have to do these complicated calorie counting diets, where people are always logging stuff into MyFitnessPal on their phone," she said. "Instead of counting calories, they could just count time."

Peterson added that prior research suggests the work associated with calorie counting makes it difficult to sustain, as people need to be educated in portion sizes and calorie levels and then need to track and log their meals.

Intermittent fasting, on the other hand, offers "a simpler rule people can follow, and it's producing the same weight loss effect as counting calories, so in my book, that's actually a big victory," Peterson said.

Dorothy Sears, a professor of nutrition at Arizona State University's College of Health Solutions, said the implication of the study isn't that intermittent fasting is an "excuse to change your diet for the worse."

"We are designed to most optimally process nutrients during the day," she said. "So let's just start by having people eat during the daytime and avoid the nighttime eating, which in itself is associated with negative health outcomes."

Sears added there's no need to "arm wrestle" about whether calorie counting or intermittent fasting is better, "but we do need to test whether time-restricted eating is as effective, and this study is showing, yes, it's effective." (Stone, "Shots," NPR, 6/26; Bendix, NBC News, 6/26)