Effectiveness of Early Time-Restricted Eating for Weight Loss, Fat Loss, and Cardiometabolic Health in Adults With Obesity: A Randomized Clinical Trial

Abstract

Importance: It is unclear how effective intermittent fasting is for losing weight and body fat, and the effects may depend on the timing of the eating window. This randomized trial compared time-restricted eating (TRE) with eating over a period of 12 or more hours while matching weight-loss counseling across groups.

Objective: To determine whether practicing TRE by eating early in the day (eTRE) is more effective for weight loss, fat loss, and cardiometabolic health than eating over a period of 12 or more hours.

Design, setting, and participants: The study was a 14-week, parallel-arm, randomized clinical trial conducted between August 2018 and April 2020. Participants were adults aged 25 to 75 years with obesity and who received weight-loss treatment through the Weight Loss Medicine Clinic at the University of Alabama at Birmingham Hospital.

Interventions: All participants received weight-loss treatment (energy restriction [ER]) and were randomized to eTRE plus ER (8-hour eating window from 7:00 to 15:00) or control eating (CON) plus ER (≥12-hour window).

Main outcomes and measures: The co-primary outcomes were weight loss and fat loss. Secondary outcomes included blood pressure, heart rate, glucose levels, insulin levels, and plasma lipid levels.

Results: Ninety participants were enrolled (mean [SD] body mass index, 39.6 [6.7]; age, 43 [11] years; 72 [80%] female). The eTRE+ER group adhered 6.0 (0.8) days per week. The eTRE+ER intervention was more effective for losing weight (-2.3 kg; 95% CI, -3.7 to -0.9 kg; P = .002) but did not affect body fat (-1.4 kg; 95% CI, -2.9 to 0.2 kg; P = .09) or the ratio of fat loss to weight loss (-4.2%; 95% CI, -14.9 to 6.5%; P = .43). The effects of eTRE+ER were equivalent to reducing calorie intake by an additional 214 kcal/d. The eTRE+ER intervention also improved diastolic blood pressure (-4 mm Hg; 95% CI, -8 to 0 mm Hg; P = .04) and mood disturbances, including fatigue-inertia, vigor-activity, and depression-dejection. All other cardiometabolic risk factors, food intake, physical activity, and sleep outcomes were similar between groups. In a secondary analysis of 59 completers, eTRE+ER was also more effective for losing body fat and trunk fat than CON+ER.

Conclusions and relevance: In this randomized clinical trial, eTRE was more effective for losing weight and improving diastolic blood pressure and mood than eating over a window of 12 or more hours at 14 weeks.

Trial registration: ClinicalTrials.gov Identifier: NCT03459703.

Figure 1.. Participant Flow Diagram

CON+ER indicates control eating window plus energy restriction group; eTRE+ER, early time-restricted eating plus energy restriction group.

Figure 2.. Adherence, Satisfaction, and Acceptability

A, Shown are the times of day (mean [SD]) that participants started eating (left end of box and left whisker) and stopped eating (right end of box and right whisker) in each group. The vertical line within the boxes indicates the median time of the eating window (averaged across all participants). The early time-restricted eating plus energy restriction (eTRE+ER) group ate over a 4.8-hour shorter window than the control plus energy restriction (CON+ER) group. B, The eTRE+ER group adhered a mean (SD) of 6.0 (0.8) days per week and was less adherent to the prescribed eating window than the CON+ER group. Data shown are raw means with 95% CIs. C, Among completers (n = 59), satisfaction with the prescribed eating window was similar between groups. Data shown are unadjusted means (boxes) with 95% CIs (whiskers), and the horizontal line within the boxes indicates the median. D, After completing the intervention, 12 participants (41%) in the eTRE+ER group planned to continue practicing eTRE, with 8 (28%) preferring to keep the original 7:00 to 15:00 schedule, and the remainder preferring to modify the window in a manner consistent with eTRE (defined as eating over a ≤10-hour window ending by 17:00). The other 8 (28%) and 9 (31%) participants wanted to practice midday TRE (mTRE; defined as eating over a ≤10-hour period ending after 17:00) or not practice TRE (defined as eating over a >10-hour period), respectively.

Figure 3.. Weight Loss and Body Composition

A, Early time-restricted eating plus energy restriction (eTRE+ER) was more effective than the control eating schedule plus energy restriction (CON+ER) for losing weight. Data shown are least-squares means and 95% CIs from linear mixed modeling with adjustment for age, sex, and race. There were no statistically significant differences between groups for body fat (B), fat-free mass (C), or the ratio of fat loss to weight loss (n = 41) (D). Data shown in panels B-D are means and 95% CIs from multiple imputation by chained equations, followed by linear regression with adjustment for age, sex, and race.