The idea of losing weight is quite appealing: limit your eating to six to eight hours a day, during which you can eat whatever you want.
Studies in mice have been shown to support so-called time-restricted eating, a form of the popular intermittent fasting diet. Small studies of obese people suggested it helped them lose weight.
But now a thorough 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 direct effect.
The conclusion, according to Dr. Ethan Weiss, a diet researcher at the University of California at San Francisco: “There’s no point in eating in a small window of time.”
The study, published Wednesday in the New England Journal of Medicine, was conducted by researchers at the University of Medicine of the South in Guangzhou, China, and included 139 obese people. Women ate between 1,200 and 1,500 calories per day, and men ate between 1,500 and 1,800 calories per day. To ensure validity, participants were required to photograph all food they ate and keep food diaries.
The two groups lost weight — 6.3 kg to 8.1 kg on average — but there was no significant difference in the amount of weight lost with each dietary strategy. There were also no significant differences between groups in measurements of waist circumference, body fat, and lean body mass.
Also, scientists found no differences in risk factors such as blood glucose levels, insulin sensitivity, blood lipids and blood pressure.
“These results indicate that caloric intake restriction explained most of the beneficial effects seen with the intermittent eating regimen,” Weiss and colleagues concluded.
The new study isn’t the first to test time-restricted feeding, but previous studies were generally smaller, or shorter in duration, and without control groups. These studies tended to conclude that people lost weight if they ate only a limited time of the day.
Weiss used to believe in intermittent fasting and said he ate only between noon and 8pm for seven years.
In previous research, he and his colleagues asked about 116 adult participants to eat three meals a day, with snacks if they were hungry, and others were told to eat whatever they wanted between noon and 8 p.m. Participants lost little weight – an average of 0.900 kg in the intermittent fasting group and 0.680 kg in the control group, a difference that is not statistically significant.
Weiss recalled that he could hardly believe the results. He asked statisticians to analyze the data four times, until he was told it wouldn’t change the results.
“I was a devotee,” he said. “It was hard to accept.”
The experiment lasted 12 weeks. Now it turns out that even a one-year study found no benefit from intermittent fasting.
Christopher Gardner, director of nutritional studies at Stanford’s Prevention Research Center, said he wouldn’t be surprised if time-limited eating occasionally worked.
“Almost every type of diet out there works for some people,” he said. “But the upshot of this new research is that when subjected to well-designed and conducted research — scientific research — it’s no more effective than simply reducing calorie intake for weight loss and health factors.”
Weight loss experts say intermittent diets probably won’t go away. “We don’t have a clear answer yet” as to whether the strategy will help people lose weight, said Courtney Peterson, a researcher at the University of Alabama at Birmingham who studies time-restricted diets.
She suspects the diet could benefit people by limiting the number of calories they can consume on a daily basis. “We just need to do bigger studies,” Peterson 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 struggle with calorie-counting diets do better when told to eat only for a limited amount of time each day. to eat.
“While this approach has not been confirmed as better, it appears to be no worse” than calorie counting, he said. “It gives patients more options for success.”
The hypothesis behind intermittent fasting is that circadian genes that would 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, is, “If you eat a little too much during the day, are you better off burning those calories than storing them?” Apovian said he would like to see a study comparing a group of subjects who eat too much throughout the day with a group of subjects who also eat too much, but with limited time.
She said she would still recommend time-restricted nutrition to patients, although “we have no evidence.”
Weiss said his own research convinced him that intermittent feeding was pointless, and that the new data bolstered his belief.
“I’ve started breakfast again,” he said. “My family says I’m much nicer.”
Translated by Luiz Roberto M. Goncalves