UCSF

IMPORTANCE Time-restricted eating has increased in popularity among people trying to lose weight. However, the efficacy and safety have not been explored in a large, prospective randomized trial.

OBJECTIVE To compare the effects of weight loss in people who are overweight and obese prescribed a time-restricted eating protocol versus standard three meals per day.

DESIGN, SETTING, AND PARTICIPANTS The Time-Restricted Eating (TREAT) study was a 12-week randomized controlled trial of men and women aged 18-64 with a body mass index of 27-43 kg/m2. The study was conducted on a custom mobile study app on the Eureka Research Platform, and participants received a Bluetooth scale for daily use. Participants lived anywhere in the United States, with a subset of participants (n=50) living within 60 miles of San Francisco who underwent comprehensive, in-person metabolic testing.

INTERVENTION Subjects were randomized to one of two eating plans and received daily reminders about their eating windows through the study app. The consistent meal timing (CMT) group was instructed to eat three structured meals per day. The time-restricted eating (TRE) group was instructed to eat ad libitum from 12:00 pm until 8:00 pm and completely abstain from caloric intake from 8:00 pm until 12:00 pm the following day (16h fast:8h eat). Specific recommendations for caloric intake or macronutrient content were not prescribed to either group, and participants were not advised to make any changes to their physical activity.

MAIN OUTCOMES AND MEASURES The primary outcome was weight loss as measured at home on the Bluetooth-connected scale. Secondary outcomes were weight loss in the in-person cohort and changes in fat mass, lean mass, fasting insulin, fasting glucose, HbA1C, total energy expenditure, and resting energy expenditure. Bonferroni-corrected alphas and confidence intervals were used to correct for multiple comparisons for secondary outcomes. All other outcomes were considered exploratory and were not corrected for multiple outcomes.

RESULTS 116 subjects (mean [SD] age, 46.5 [10.5] years), participated in the study. There was a significant decrease in weight in the TRE (-0.94kg, 95% CI, -1.68, -0.20, p=0.013), but no significant change in the CMT group (-0.68kg, 95% CI, -1.41, 0.05, p=0.07) or between groups (-0.26kg, 95% CI, -1.30, 0.78, p=0.63). In the in-person cohort, (n=25 TRE, n=25 CMT), there was a significant within-group decrease in weight in the TRE group (-1.70kg, 95% CI, -2.56, -0.83, p<0.001), but no significant changes in any of the other secondary outcomes. There was a significant within-group decrease in lean mass in the TRE group (-1.10kg, 95% CI, -1.73, -0.48, p<0.001). There was also a significant difference in appendicular lean mass index between groups (-0.162kg/m2, 95% CI, -0.274, -0.050, p=0.005).

CONCLUSIONS AND RELEVANCE Prescribing TRE to people who are overweight and obese led to modest weight loss, but there was no difference in weight loss when compared to those randomized to CMT. Moreover, the majority of weight lost in people randomized to TRE came from loss of lean mass rather than fat mass. The mechanism(s) underlying this phenomenon is unknown, and future studies will be aimed at exploring the relationship between fasting and lean body mass.