It's a been a popular fitness trend in recent years—people limit their meals to a certain window each day. Small-scale studies suggested this form of intermittent fasting helped people lose weight, but a comprehensive new study concludes otherwise, reports the New York Times. The yearlong study out of Southern Medical University in Guangzhou, China, is newly published in the New England Journal of Medicine. Researchers put 139 men and women who already were overweight on a restricted diet (up to 1,500 calories per day for women and 1,800 for men). Some were told to eat only between 8am and 4pm and others could eat whenever they wanted, per CNN. They all had to keep strict food diaries, including photographs of meals.
In the end, participants in both groups lost an average of about 15 pounds, but the researchers say that was because of the restricted calories. They saw no difference between those who ate during the restricted window and the others.
- A "regimen of time-restricted eating was not more beneficial with regard to reduction in body weight, body fat, or metabolic risk factors than daily calorie restriction," they write in the study.
- The upshot is "there is no benefit to eating in a narrow window," Dr. Ethan Weiss of the University of California, San Francisco, tells the Times. The newspaper notes that Weiss himself had restricted his own diet in a similar manner for seven years.
- "Bottom line, the determinant of weight loss, as well as reductions in body fat, visceral fat, blood pressure, and glucose and lipid levels, is dependent on reducing calorie intake, regardless of the distribution of food and beverages consumed throughout the day," Alice Lichtenstein of Tufts University tells CNN.
- Still, don't expect time-restricted eating to go away. Researchers not involved in the China study say it could work for some simply by making it easier to track daily calories. More large studies could shed further light.