The idea of losing weight is very appealing: limit your eating to a period of six to eight hours a day, during which you can have whatever you want.
Studies in mice appeared to support so-called time-restricted eating, a form of the popular intermittent fasting diet. Small studies of obese people suggested it could help shed pounds.
But now a rigorous one-year study in which people followed a low-calorie diet between 8 a.m. and 4 p.m. or consumed the same number of calories at any time of the day has found no effect.
Bottom line, said Dr. Ethan Weiss, a diet researcher at the University of California, San Francisco: “There’s no point in eating in a narrow window.”
The study, published Wednesday in the New England Journal of Medicine, was led 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 consumed 1,500 to 1,800 calories daily. To ensure compliance, participants were required to photograph every piece of food they ate and keep food diaries.
Both groups lost weight — about 14 to 18 pounds on average — but there was no significant difference in the amount of weight lost with either diet strategy. There were also no significant differences between the groups in measures of waist circumference, body fat and lean body mass.
The scientists also found no differences in risk factors such as blood glucose levels, insulin sensitivity, blood lipids or blood pressure.
“These results indicate that calorie restriction explained most of the beneficial effects seen with the time-restricted eating regimen,” concluded Dr. Weiss and his colleagues.
The new study isn’t the first to test time-restricted eating, but previous studies were often smaller, shorter in duration, and without control groups. That research mostly concluded that people lost weight by eating only for a limited period of the day.
dr. Weiss himself used to be a real adherent of time-restricted eating, saying that for seven years he only ate between noon and 8 p.m.
In previous research, he and his colleagues asked some of the 116 adult participants to eat three meals a day, with snacks if they got hungry, and others were instructed to eat whatever they wanted between noon and 8 p.m. Participants lost a small amount of weight — an average of two pounds in the time-restricted eating group and 1.5 pounds in the control group, a difference that was not statistically significant.
In an interview, Dr. Weiss realized he could hardly believe the results. 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 said. “This was hard to accept.”
That experiment lasted only 12 weeks. Now it seems that even a one-year study has failed to find a benefit in time-restricted eating.
dr. Christopher Gardner, director of nutritional studies at the Stanford Prevention Research Center, said he wouldn’t be surprised if time-limited eating did occasionally work.
“Almost every type of diet out there works for some people,” he said. “But the conclusion supported by this new research is that when subjected to well-designed and conducted research — scientific research — it helps no more than simply reducing daily calorie intake for weight loss and health factors.”
Weight loss experts said time-restricted diets probably won’t go away. “We don’t have a clear answer yet” about whether the strategy will help 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,” said Dr. peterson.
dr. Louis J. Aronne, director of the Comprehensive Weight Control Center at Weill Cornell Medicine in New York, said that, in his experience, some people who have trouble counting calories do better when told to eat alone during a workout. limited time per day.
“While that approach hasn’t been shown to be better, it doesn’t appear to be any worse” than calorie counting, he said. “It gives patients more options for success.”
The hypothesis behind time-restricted eating is that circadian genes thought to increase metabolism are turned on 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 bit during the day, are you better off burning those calories than storing them?” dr. Apovian said she would like to see a study comparing a group of subjects who ate too much throughout the day with a time-bound group of subjects who also ate too much.
She said she would still recommend time-limited eating to patients, she said, even though we don’t have any evidence.
for dr. Weiss said he was convinced by his own research and said the new data reinforced his belief that time-restricted eating offers no benefit.
“I started eating breakfast,” he said. “My family says I’m a lot nicer.”
