Scientists find no benefit to time-restricted diets

Scientists find no benefit to time-restricted diets

The idea of ​​weight loss is quite appealing: limit your eating to six to eight hours a day, during which you can eat whatever you want.

Studies in mice seemed to support what is called time-restricted eating, a popular form of intermittent fasting diet. Small studies in obese people have suggested it may help with weight loss.

But now, a rigorous year-long study in which people ate a low-calorie diet between 8 a.m. and 4 p.m. or ate the same number of calories at all times of the day found no effect.

Ultimately, said Dr. Ethan Weiss, a dietary researcher at the University of California, San Francisco, “There’s no benefit to eating within a narrow window.”

The study, published Wednesday in the New England Journal of Medicine, was conducted by researchers at Southern Medical University in Guangzhou, China, and included 139 obese people. Women ate 1,200 to 1,500 calories per day and men ate 1,500 to 1,800 calories per day. To ensure compliance, participants had to photograph every piece of food they ate and keep a food diary.

Both groups lost weight – an average of around 14 to 18 pounds – but there was no significant difference in the amounts of weight lost with either dieting strategy. There were also no significant differences between groups in measurements of waist circumference, body fat, and lean body mass.

The scientists also found no difference in risk factors such as blood sugar, insulin sensitivity, blood lipids or blood pressure.

“These results indicate that calorie restriction explained most of the beneficial effects seen with the time-restricted diet,” Dr. Weiss and colleagues concluded.

The new study is not the first to test the time-restricted diet, but previous studies have often been smaller, shorter in duration and without control groups. This research tended to conclude that people lost weight by only eating for a limited period of the day.

Dr. Weiss himself was a real proponent of time-restricted eating and said that for seven years he only ate between noon and 8 p.m.

In previous research, he and his colleagues instructed some of the 116 adult participants to eat three meals a day, with snacks if they were hungry, and others were instructed to eat whatever they wanted between noon. and 8 p.m. The participants lost some weight. – an average of two pounds in the time-restricted feeding group and 1.5 pounds in the control group, a difference that was not statistically significant.

In an interview, Dr. Weiss recalled that he found the results hard to believe. He asked the statisticians to analyze the data four times, until they told him that further work would not change the results.

“I was a devotee,” he says. “It was a hard thing to accept.”

This experience only lasted 12 weeks. Now, it looks like even a year-long study failed to find any benefit in time-restricted eating.

Dr. Christopher Gardner, director of nutrition studies at the Stanford Prevention Research Center, said he wouldn’t be surprised if time-restricted feeding nevertheless worked on occasion.

“Almost all types of diets work for some people,” he said. “But the homecoming supported by this new research is that when subjected to a properly designed and conducted study – scientific investigation – it is no more helpful than simply reducing daily caloric intake for weight loss. weight and health factors.

Weight loss experts say time-limited diets aren’t going to go away. “We don’t have a clear answer yet” about whether the strategy helps people lose weight, said Courtney Peterson, a researcher at the University of Alabama at Birmingham who studies time-restricted eating.

She suspects the diet could benefit people by limiting the number of calories they can consume each day. “We just need to do bigger studies,” Dr. Peterson said.

Dr. Louis J. Aronne, director of the Comprehensive Weight Control Center at Weill Cornell Medicine in New York City, said that in his experience, some people who have trouble with calorie diets do better if they are simply told not to. eat only for a limited period of time each day.

“While this approach hasn’t been shown to be better, it doesn’t appear to be worse” than calorie counting, he said. “It gives patients more options to succeed.”

The hypothesis behind the time-restricted diet is that circadian genes thought to increase metabolism are activated during the day, said Dr. Caroline Apovian, co-director of the Center for Weight Management and Wellness at Brigham and Women’s Hospital in Boston.

The question for researchers, she added: “If you eat a little too much during the day, are you more able to burn those calories rather than store them?” Dr. Apovian said she would like to see a study that compares a group of subjects who overeat all day with a group of subjects who overeat and overeat.

She said she would always recommend time-restricted feeding to patients, she said, even though “we don’t have proof.”

For Dr. Weiss, he said he was convinced by his own study and said the new data reinforced his belief that time-restricted feeding offers no benefit.

“I started having breakfast,” he said. “My family says I’m a lot nicer.”

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