Participants with obesity who engaged in any of three 8-hour, time-restricted eating schedules experienced weight loss and improvements in cardiovascular and metabolic health compared to participants with obesity in the Mediterranean diet control group. Members of the time-restricted eating groups also followed their regimens more faithfully than those on the Mediterranean diet. The findings, published in Nature Medicine, suggest time-restricted eating provides beneficial effects irrespective of the time of day individuals have their meals. The research addresses a long-standing question in the study of caloric restriction.

Numerous scientific studies have suggested restricting daily food intake to an 8-hour timeframe is an effective dietary intervention to address obesity, but the optimal time of day for eating remained in debate. To address the question, scientists from NIA, NIH National Institute of Diabetes and Digestive and Kidney Diseases, and the Universities of Granada and Navarra in Spain designed an experimental study that included 197 men and women with obesity. The researchers compared three 8-hour eating windows simultaneously: morning (49 participants), afternoon (52 participants), and whenever they chose (47 participants). As long as 16 hours of fasting were maintained, the time-restriction eating schedule was acceptable. The control group (49 participants) followed the Mediterranean diet and did not engage in time-restricted eating.

The researchers gathered metrics, including body weight, and took blood samples for metabolic analysis. Participants wore a glucose monitoring device at the beginning and end of the three-month study, so scientists knew when participants were eating. The team also used MRI to measure changes in visceral body fat, i.e., fat stored near internal organs, and subcutaneous body fat, which is fat stored under the skin in the buttocks, thighs, hips, and abdomen. Visceral body fat is associated with cardiometabolic diseases such as heart attack, stroke, diabetes, and insulin resistance.

The results showed all three time-restricted eating groups achieved more weight loss — averages of 5.3 pounds, 6.4 pounds, and 6.8 pounds, respectively — than the control group. There were no differences among the morning, afternoon, and self-selected time-restricted eating groups and the Mediterranean diet control in reducing visceral body fat. However, the morning group demonstrated a greater reduction in subcutaneous body fat and improved cardiometabolic health markers, such as lower fasting glucose levels, than the control group.

The study suggests that regardless of when adults with obesity restrict their eating, the strategy appears to be a safe and well-tolerated dietary approach that leads to weight loss and other positive health outcomes. However, the study is based on a European cohort and does not completely reflect the dietary patterns of the American population, especially those at highest risk for obesity. Future studies should confirm whether this finding is true for a racially and ethnically diverse American cohort whose dietary preferences, habits, and socioeconomic status may differ from the European cohort.

Reference: Dote-Montero M, et al. Effects of early, late and self-selected time-restricted eating on visceral adipose tissue and cardiometabolic health in participants with overweight or obesity: A randomized controlled trial. Nature Medicine. 2025. Epub Jan. 7. doi: 10.1038/s41591-024-03375-y.