The idea of weight loss is quite appealing: Limit your eating to a period of six to eight hours a day, during which you can eat 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 people with obesity have suggested that it can help them lose weight.
But now, a rigorous one-year study in which people followed a low-calorie diet between 8 am and 4 pm or consumed the same number of calories at any time of day failed to find an effect.
The end result, said Dr. Ethan Weiss, a diet researcher at the University of California, San Francisco: “There’s no benefit to 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 people with obesity. Women ate 1,200 to 1,500 calories a day and men ate 1,500 to 1,800 calories a day. To ensure compliance, participants were required to photograph every morsel of food they ate and keep food diaries.
Both groups lost weight — an average of about 14 to 18 pounds — but there was no significant difference in the amounts of weight lost with either diet 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 differences in risk factors such as blood glucose levels, insulin sensitivity, blood lipids or blood pressure.
“These results indicate that restriction of caloric intake explained most of the beneficial effects seen with the time-restricted diet,” concluded Dr. Weiss and his colleagues.
The new study is not the first to test time-restricted feeding, but previous studies were generally smaller, shorter in duration and without control groups. That research tended to conclude that people lost weight by eating only a limited amount of time during the day.
Dr himself. Weiss used to be a true believer in time-restricted eating and said that for seven years he only ate between noon and 8pm.
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 told to eat whatever they wanted between noon and 8 pm. – 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 could hardly believe the results. He asked the statisticians to analyze the data four times, until he was told that more work would not change the results.
“I was a devotee,” he said. “That was a hard thing to accept.”
This experiment lasted only 12 weeks. Now, it appears that even a year-long study failed to find a benefit to 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 eating worked every now and then.
“Almost every type of diet works for some people,” he said. “But the conclusion supported by this new research is that when subjected to a properly designed and conducted study – scientific investigation – it is no more useful than simply reducing daily calorie intake for weight loss and health factors.”
Weight loss experts said time-restricted diets are unlikely to go away. “We still don’t have a clear answer” 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 can benefit people by limiting the number of calories they have the opportunity to consume each day. “We just need to do larger studies,” Peterson said.
The Doctor. 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 problems with calorie-counting diets do better if they are told to eat only for a period of time. limited time each day.
“While this approach hasn’t been shown to be any better, it doesn’t appear to be any worse” than calorie counting, he said. “This gives patients more options for success.”
The hypothesis behind time-restricted eating is that circadian genes that are supposed 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 the researchers, she added, “If you eat too much during the day, will you be better able to burn those calories instead of storing them?” Dr. Apovian said she would like to see a study that compares a group of individuals who overeat throughout the day with a group of individuals who also overeat.
She said she would still recommend time-restricted eating to patients, she said, even though “we don’t have proof.”
for Dr. Weiss, he said he was persuaded by his own study and said the new data reinforced his belief that time-restricted eating offers no benefit.
“I started having breakfast,” he said. “My family says I’m much nicer.”