The idea of losing weight is quite appealing: limit eating to a period of six to eight hours each dayduring which you can eat whatever you want.
Studies in mice seem to support so-called time-restricted feeding, a form of the popular intermittent fasting diet. Small studies in obese people suggested that it might help lose pounds.
But now a rigorous one-year study of duration 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, found no effect.
The bottom line, according to Dr. Ethan Weiss, a diet researcher at the University of California, San Francisco: “There is no benefit to eating in a restricted time window.”
The study, published in the journal New England Journal of Medicinewas led by researchers from the Southern Medical University in Guangzhou, China, and included 139 people with obesity.
Women ate between 1,200 and 1,500 calories a day, and men between 1,500 and 1,800 calories a day. To ensure compliance, participants were asked to photograph each piece of food they ate and to keep a food diary.
Both groups lost weight -an average of between 4 and 5 kilos-, but there were no significant differences in the amounts of weight lost with each diet strategy. There were also no significant differences between the groups in measurements of waist circumference, body fat, and lean body mass.
The scientists also found no difference in risk factors such as blood glucose levels, insulin resistance, blood lipids or blood pressure.
Time-restricted eating is one of the most popular modalities among those who fast. Photo: Shutterstock.
Reduce caloric intake
“These results indicate that the caloric intake restriction explains most of the beneficial effects seen with the restricted feeding regimen,” Weiss and colleagues concluded.
The new study isn’t the first to test time-restricted feeding, but previous studies tended to be smaller, of shorter duration, and with no control groups. Those investigations tended to conclude that people lost weight by eating only during a limited period of the day.
Weiss he was a true believer on time-restricted eating and said that for seven years he ate only between noon and 8 p.m.
In earlier research, Weiss and her colleagues asked some of the 116 adult participants to eat three meals a day, with snacks if they were hungry, and instructed others to eat whatever they wanted between noon and 8 p.m.
Participants lost little weight: a mean of 900 grams in the time-restricted feeding group, and 700 grams in the control group, a difference that was not statistically significant.
Weiss recalls that she 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. “It was a difficult thing to accept.”
That experiment lasted only 12 weeks. Now, it appears that even a year-long study has failed to find a benefit to time-restricted eating.
Christopher Gardner, director of nutrition studies at the Stanford Prevention Research Center, said he wouldn’t be surprised if time-restricted eating worked, but sometimes.
“Just about every type of diet out there works for some people,” he said. “But the conclusion that this new research supports is that, when subjected to a properly designed and conducted study – scientific research – no more helpful than simply reducing daily intake of calories for weight loss and health factors.
Weight-loss experts said time-restricted diets are unlikely to go away. “We don’t have a clear answer yet” whether the strategy helps people lose weight, said Courtney Peterson, a researcher at the University of Alabama at Birmingham who studies time-restricted eating.
Weight loss was similar in both groups. Illustrative photo Shutterstock.
He suspects that the diet could benefit people by limiting the number of calories they can consume each day. “We have to do larger studiesPeterson said.
Dr. Louis J. Aronne, director of the Center for Comprehensive Weight Management at Weill Cornell Medicine in New York, said that in his experience, some people who have trouble with calorie counting diets do better if simply tell them eat only for a limited period of time each day.
Although that approach was not shown to be better, doesn’t seem to be worsethan counting calories, he said. “It gives patients more options for success.”
The hypothesis behind the time restriction is that circadian genes thought to increase metabolism are activated during daylight hours, said Dr. Caroline Apovian, co-director of the Center for Weight Management and Wellness at Brigham and Women’s Hospital. from Boston.
The question for the researchers is: “If you eat a little more during daylight hours, are you better able to burn those calories instead of storing them?” Apovian said he would like to see a study comparing a group of people who overeat throughout the day with a group of subjects who also overeat with a time restriction.
He said he would continue to recommend time-restricted feeding to patients, though “we have no evidence”.
As for Weiss, he said he was convinced by his own study and said the new data reinforced his belief that there is no benefit to the time restriction.
“I started breakfast”, said. “My family says I’m much nicer.”
By Gina Kolata ©The New York Times
Translation: Patricia Sar