, indicate the results of a randomized controlled trial.
The study involved more than 200 individuals randomized to one of three groups: eat only in the morning (from 8:00 a.m. to noon) followed by 20 hours of fasting 3 days per week and eat as desired on the other days; daily calorie restriction to 70% of requirements; or standard weight loss advice.
The IF plus early time-restricted eating intervention was associated with a significant improvement in a key measure of glucose control versus calorie restriction at 6 months, while both interventions were linked to benefits in terms of cardiovascular risk markers and body composition, compared with the standard weight loss advice.
However, the research, published in Nature Medicine, showed that the additional benefit of IF plus early time-restricted eating did not persist, and less than half of participants were still following the plan at 18 months, compared with almost 80% of those in the calorie-restriction group.
“Following a time-restricted, IF diet could help lower the chances of developing type 2 diabetes,” senior author Leonie K. Heilbronn, PhD, University of Adelaide, South Australia, said in a press release.
This is “the largest study in the world to date, and the first powered to assess how the body processes and uses glucose after eating a meal,” with the latter being a better indicator of diabetes risk than a fasting glucose test, added first author Xiao Tong Teong, a PhD student, also at the University of Adelaide.
“The results of this study add to the growing body of evidence to indicate that meal timing and fasting advice extends the health benefits of a restricted-calorie diet, independently from weight loss, and this may be influential in clinical practice,” Ms. Teong added.
Adherence difficult to IF plus early time-restricted eating
Asked to comment, Krista Varady, PhD, said that the study design “would have been stronger if the time-restricted eating and IF interventions were separated” and compared.
“Time-restricted eating has been shown to naturally reduce calorie intake by 300-500 kcal/day,” she said in an interview, “so I’m not sure why the investigators chose to combine [it] with IF. It ... defeats the point of time-restricted eating.”
Dr. Varady, who recently coauthored a review of the clinical application of IF for weight loss, also doubted whether individuals would adhere to combined early time-restricted eating and IF. “In all honesty, I don’t think anyone would follow this diet for very long,” she said.
She added that the feasibility of this particular approach is “very questionable. In general, people don’t like diets that require them to skip dinner with family/friends on multiple days of the week,” explained Dr. Varady, professor of nutrition at the University of Illinois, Chicago. “These regimens make social eating very difficult, which results in high attrition.
“Indeed, evidence from a recent large-scale observational study of nearly 800,000 adults shows that Americans who engage in time-restricted eating placed their eating window in the afternoon or evening,” she noted.
Dr. Varady therefore suggested that future trials should test “more feasible time-restricted eating approaches,” such as those with later eating windows and without “vigilant calorie monitoring.”
“These types of diets are much easier to follow and are more likely to produce lasting weight and glycemic control in people with obesity and prediabetes,” she observed.