Studies have found, for example, that overweight adults lose more weight and have greater improvements in their cardiovascular risk factors when they eat a large breakfast, a modest lunch and a light dinner, compared to when they eat a small breakfast and a big dinner.
“It could be that the benefits of time-restricted eating are smaller than we thought, or that you just get better results when you eat earlier in the day,” said Courtney Peterson, a researcher at the University of Alabama at Birmingham who studies intermittent fasting and who was not involved in the new study. “The jury is still out.”
Many cultures around the world practice fasting for religious or spiritual reasons. But fasting became popular for health reasons after small studies suggested it promotes longevity and a wide range of metabolic benefits, such as improved cholesterol profiles and reductions in insulin resistance. Some of the other common forms of intermittent fasting are alternate day fasting, in which followers eat no more than 500 calories every other day, and the 5:2 diet, which entails eating normally for five days a week and fasting for two.
Many people, however, have trouble going an entire day with little or no food. Krista Varady, a professor of nutrition at the University of Illinois, Chicago, has found in her research that people lose weight more slowly with time-restricted eating than other forms of fasting but that it is generally the easiest form of fasting to adopt. People tend to eat 300 to 500 calories fewer per day when they restrict themselves to an eight-hour window, said Dr. Varady, who was not involved in the new research.
“The best part is there are no limitations during the window,” she said. “There is no carb or calorie counting, and people don’t have to switch out all the food in their pantries.”
Dr. Varady said she is planning to start a yearlong study of time-restricted eating in the near future. “I find it fascinating that this diet has become so popular and there are so few studies,” she said.
Dr. Weiss got interested in time-restricted eating after learning about research that showed that mice provided round-the-clock access to high-fat, high-sugar foods got fat and sick, while mice that ate the same foods in an eight-hour daily window were protected against obesity and metabolic disease. In his own experience, Dr. Weiss found that skipping breakfast and eating between noon and 8 p.m. was not very difficult.