Effects of Time-Restricted Eating on Weight Loss and Other Metabolic Parameters in Women and Men With Overweight and Obesity: The TREAT Randomized Clinical Trial

Abstract

Importance: The efficacy and safety of time-restricted eating have not been explored in large randomized clinical trials.

Objective: To determine the effect of 16:8-hour time-restricted eating on weight loss and metabolic risk markers.

Interventions: Participants were randomized such that the consistent meal timing (CMT) group was instructed to eat 3 structured meals per day, and 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.

Design, setting, and participants: This 12-week randomized clinical trial including men and women aged 18 to 64 years with a body mass index (BMI, calculated as weight in kilograms divided by height in meters squared) of 27 to 43 was conducted on a custom mobile study application. Participants received a Bluetooth scale. Participants lived anywhere in the United States, with a subset of 50 participants living near San Francisco, California, who underwent in-person testing.

Main outcomes and measures: The primary outcome was weight loss. Secondary outcomes from the in-person cohort included changes in weight, fat mass, lean mass, fasting insulin, fasting glucose, hemoglobin A1c levels, estimated energy intake, total energy expenditure, and resting energy expenditure.

Results: Overall, 116 participants (mean [SD] age, 46.5 [10.5] years; 70 [60.3%] men) were included in the study. There was a significant decrease in weight in the TRE (-0.94 kg; 95% CI, -1.68 to -0.20; P = .01), but no significant change in the CMT group (-0.68 kg; 95% CI, -1.41 to 0.05, P = .07) or between groups (-0.26 kg; 95% CI, -1.30 to 0.78; P = .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 (-1.70 kg; 95% CI, -2.56 to -0.83; P < .001). There was also a significant difference in appendicular lean mass index between groups (-0.16 kg/m2; 95% CI, -0.27 to -0.05; P = .005). There were no significant changes in any of the other secondary outcomes within or between groups. There were no differences in estimated energy intake between groups.

Conclusions and relevance: Time-restricted eating, in the absence of other interventions, is not more effective in weight loss than eating throughout the day.

Trial registration: ClinicalTrials.gov Identifiers: NCT03393195 and NCT03637855.

Figure 1.. CONSORT Flow Diagram

CMT indicates consistent meal timing group; TRE, time-restricted eating group. CONSORT flow diagram describing process of participant recruitment, enrollment, randomization, and data analysis. Participants were excluded from participating if they (1) were older than 64 years (n = 5), (2) had a body mass index (calculated as weight in kilograms divided by height in meters squared) less than 27 (n = 348) or greater than 43 (n = 72), (3) did not regularly consume breakfast (n = 566), (4) were unwilling or unable to skip breakfast (n = 761), (5) had a current or past cancer diagnosis (n = 21), (6) were breastfeeding, pregnant, or planned to be pregnant within 6 months (n = 21), (7) had current diagnosis of type 1 or type 2 diabetes mellitus (n = 177), (8) were taking glucose-lowering drugs (n = 133) or weight loss pills (n = 116), (9) had a history of gastric bypass or any weight-loss surgery (n = 66), (10) had a weight fluctuation of more than 15% in past 5 years (n = 467), (11) had a history of anorexia or bulimia (n = 39), (12) frequently traveled across time zones (n = 99) or worked unusual work hours (n = 182), or (13) were unable to fast for prolonged periods (n = 168).

Figure 2.. Adherence and Weight Change in the Total Cohort

A, Participants were sent daily adherence surveys through the study application (“Did you adhere to your eating plan on the previous day?” Yes/No). Responses from all completed surveys were analyzed. The percent adherence to protocol is shown over time for consistent meal timing group (CMT) (dashed blue line; n = 41) and time-restricted eating (TRE) participants (solid orange line; n = 44). B, Individual daily weight measurements as recorded from the at-home scale are shown for each participant over time throughout the duration of the study. The individual weight measurements are show as maroon dots for the CMT group (n = 57) and blue dots for TRE group (n = 59). The solid lines represent weight over time as determined from the linear mixed model. C, Waterfall plot showing percent weight change for each participant from the total cohort in the CMT group (left) and TRE group (right).