The idea of losing weight is tempting: limit your meals to six to eight hours a day, during which time you can eat whatever you want.
Studies in rats appeared to support so-called time-restricted eating, a form of the popular intermittent fasting diet. Small studies of obese people suggested that it helped them lose weight.
But now a year in a rigorous 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, there was no direct effect.
The findings came from a diet researcher at the University of California at San Francisco, Dr. According to Ethan Weiss: “There is no benefit to eating in a narrow window of time.”
The study, published Wednesday in the New England Journal of Medicine, was carried out by researchers from the University of Medicine of the South in Guangzhou, China, and involved 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 validity, participants had to photograph all the foods they ate and keep a food diary.
Both groups lost weight – an average of 6.3 kg to 8.1 kg – but there was no significant difference in the amount of weight lost with each dietary strategy. There were no significant differences between groups in waist circumference, body fat and lean body measurements.
The scientists found no difference in risk factors such as blood sugar levels, insulin sensitivity, blood lipids and blood pressure.
“These results indicate that restriction of caloric intake explained most of the beneficial effects seen with the intermittent eating regimen,” concluded Weiss and colleagues.
The new study isn’t the first to test time-restricted eating, but previous studies were generally shorter, or of shorter duration, and without control groups. These surveys concluded that people lost weight if they ate only for a limited time of the day.
Weiss believed in intermittent fasting and said that for seven years he ate only between 12 noon and 8 pm.
In previous research, he and his colleagues asked about 116 adult participants to have three meals a day with breakfast when they felt hungry, and others were asked to eat whatever they wanted between 12 p.m. and 8 p.m. . The 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 the statisticians to analyze the data four times, until he was told that it would not change the result.
“I was a devotee,” he said. “It was a hard thing to accept.”
The experiment lasted for 12 weeks. Now, it appears that even a year-long study found no benefit from intermittent fasting.
Christopher Gardner, director of nutrition studies at Stanford’s Prevention Research Center, said he wouldn’t be surprised if time-restricted eating sometimes works.
“Almost every type of diet works for some people,” he said. “But the result of this new research is that when an appropriately designed and conducted study – subject to scientific scrutiny – it is no more effective than reducing caloric intake for weight loss and health factors.”
Weight loss experts say that intermittent eating is unlikely 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 diets.
She suspects that the diet may benefit people by limiting the number of calories they have the opportunity to consume per day. “We just need to do bigger studies,” Peterson said.
Director of the Center for Comprehensive Weight Management at Weill Cornell Medicine in New York, Dr. Louis J. Aaron said that in his experience some people who struggle with calorie-counting diets do better when they are told to eat only during limited periods of time.
“While this approach has not been confirmed as better, it does not appear to be 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 daylight hours, said Dr., co-director of the Center for Weight Management and Wellness at Brigham and Women’s Hospital in Boston. Caroline Apovian said.
The question for researchers, he said, is, “If you eat a little bit more during the day, can you burn those calories better than you store them?” Apovian said she would like to see a study that compared a group of subjects who ate more throughout the day with a group of subjects who ate more, but with a time restriction.
She said she would still recommend time-restricted diets to patients, although “we have no evidence.”
Weiss said he was convinced from his own study that intermittent feeding had no benefit, and the new data reinforced his belief.
“I started having breakfast again,” he said. “My family says I’m great.”
Translated by Luiz Roberto M. Gonsalves