Can trial be applied to a wider population?
According to Blandine Laferrère, MD, PhD, and Satchidananda Panda, PhD, of Columbia University Irving Medical Center, New York, and the Salk Institute for Biological Studies, La Jolla, Calif., respectively, “the results of the trial suggest that calorie restriction combined with time restriction, when delivered with intensive coaching and monitoring, is an approach that is as safe, sustainable, and effective for weight loss as calorie restriction alone.”
Yet Dr. Laferrère and Dr. Panda also expressed skepticism about broader implementation of a similar regime.
“The applicability of this trial to wider populations is debatable,” they wrote in an accompanying editorial. “The short time period for eating at baseline may be specific to the population studied, since investigators outside China have reported longer time windows. The rigorous coaching and monitoring by trial staff also leaves open the question of whether time-restricted eating is easier to adhere to than intentional calorie restriction. Such cost-benefit analyses are important for the assessment of the scalability of a lifestyle intervention.”
Duration is trial’s greatest strength
Kristina Varady, PhD, professor of nutrition in the department of kinesiology and nutrition at the University of Illinois at Chicago, said the “key strength” of the trial was its duration, at 12 months, making it the longest time-restricted eating trial to date”; however, she was critical of the design.
Dr. Kristina Varady
“Quite frankly, I’m surprised this study got into such a high-caliber medical journal,” Dr. Varady said in a written comment. “It doesn’t even have a control group! It goes to show how popular these diets are and how much people want to know about them.”
She also noted that “the study was flawed in that it didn’t really look at the effects of true time-restricted eating.” According to Dr. Varady, combining calorie restriction with time-restricted eating “kind of defeats the purpose” of a time-restricted diet.
“The main benefit of time-restricted eating is that you don’t need to count calories in order to lose weight,” Dr. Varady said, citing two of her own studies from 2018 and 2020. “Just by limiting the eating window to 8 hours per day, people naturally cut out 300-500 calories per day. That’s why people like [time-restricted eating] so much.”
Dr. Varady was also “very surprised” at the adherence data. At 1 year, approximately 85% of the patients were still following the protocol, a notably higher rate than most dietary intervention studies, which typically report adherence rates of 50-60%, she said. The high adherence rate was particularly unexpected because of the 8:00 a.m.–4:00 p.m. eating window, Dr. Varady added, since that meant skipping “the family/social meal every evening over 1 whole year!”
The study was funded by the National Key Research and Development Project and others. The study investigators reported no conflicts of interest. Dr. Varady disclosed author fees from the Hachette Book group for her book “The Every Other Day Diet.”