Effect of Time-Restricted Eating on Weight Loss in Adults With Type 2 Diabetes: A Randomized Clinical Trial

IMPORTANCE: Time-restricted eating (TRE) has become increasingly popular, yet longer-term randomized clinical trials have not evaluated its efficacy and safety in patients with type 2 diabetes (T2D). OBJECTIVE: To determine whether TRE is more effective for weight reduction and glycemic control than daily calorie restriction (CR) or a control condition in adults with T2D. DESIGN, SETTING, AND PARTICIPANTS: This 6-month, parallel-group, randomized clinical trial was performed between January 25, 2022, and April 1, 2023, at the University of Illinois Chicago. Participants were aged 18 to 80 years with obesity and T2D. Data analysis was based on intention to treat. INTERVENTIONS: Participants were randomized to 1 of 3 groups: 8-hour TRE (eating 12 to 8 pm only, without calorie counting), CR (25% energy restriction daily), or control. MAIN OUTCOMES AND MEASURES: The primary outcome measure was change in body weight by month 6. Secondary outcomes included changes in hemoglobin A(1c) (HbA(1c)) levels and metabolic risk factors. RESULTS: Seventy-five participants were enrolled with a mean (SD) age of 55 (12) years. The mean (SD) body mass index (calculated as weight in kilograms divided by height in meters squared) was 39 (7) and the mean (SD) HbA(1c) level was 8.1% (1.6%). A total of 53 participants (71%) were women. One participant (1%) was Asian, 30 (40%) were Hispanic White, 40 (53%) were non-Hispanic Black, and 4 (5%) were non-Hispanic White. Participants in the TRE group were adherent with their eating window on a mean (SD) of 6.1 (0.8) days per week, and 17 (68%) in the CR group were adherent with their prescribed calorie goals over 6 months. The mean (SD) reduction in energy intake was −313 (509) kcal/d for TRE, −197 (426) kcal/d for CR, and −16 (439) kcal/d for controls. By month 6, body weight decreased significantly in the TRE group (−3.56% [95% CI, −5.92% to −1.20%]; P = .004) but not the CR group (−1.78% [95% CI, −3.67% to 0.11%]; P = .06), relative to controls. Levels of HbA(1c) decreased in the TRE (−0.91% [95% CI, −1.61% to −0.20%]) and CR (−0.94% [95% CI, −1.59% to −0.30%]) groups, relative to controls, with no differences between the TRE and CR groups. Time in euglycemic range, medication effect score, blood pressure, and plasma lipid levels did not differ among groups. No serious adverse events were reported. CONCLUSIONS AND RELEVANCE: This randomized clinical trial found that a TRE diet strategy without calorie counting was effective for weight loss and lowering of HbA(1c) levels compared with daily calorie counting in a sample of adults with T2D. These findings will need to be confirmed by larger RCTs with longer follow-up. TRIAL REGISTRATION: ClinicalTrials.gov Identifier: NCT05225337