Similar body composition outcomes following volumetric diet and time-restricted eating in middle-aged individuals: a 12-week randomized controlled trial.

Introduction: Overweight and obesity are increasing global challenges associated with severe health risks. Lifestyle factors like easy access to high-caloric foods and a decrease in physical activity contribute to weight gain. The increase in fat mass (FM) and decrease in lean body mass (LBM) are supported by age-related changes in body composition by the age of 30. Two dietary strategies, the volumetrics diet (VD) and time-restricted eating (TRE), have shown promise in achieving sustainable loss of body weight (BW) and FM without requiring food group exclusions or portion reductions. This study aimed to compare the impact of VD and TRE on body composition parameters and their adherence rate in middle-aged normal-weight to overweight physically active people over 12 weeks.

Methods: In this randomized controlled trial, 37 physically active participants were allocated to either VD or TRE (VD: n = 21, age: 39.48 ± 8.83 years, body mass index (BMI): 25,38 ± 4.37 kg/m²; TRE: n = 16, age: 42.06 ± 8.47, BMI: 26.38 ± 2.81 kg/m²). Participants followed their assigned dietary strategy for 12 weeks while documenting their daily food intake using the FDDB app. Adherence to the diets was self-reported weekly. The VD group consumed meals with an energy density ≤ 1.5 kcal/g and the TRE group restricted calorie intake to an 8-hour window (11:30 AM-7:30 PM). Measurements of BW, FM, LBM, BMI, waist circumference (WC) and hip circumference (HC) were taken at baseline (T0) and after 4 (T1), 8 (T2) and 12 weeks (T3). Statistical analysis included linear mixed-effect models to compare time, group and interaction effects on body composition.

Results: Both VD and TRE groups showed significant reductions in BW (p = 0.0002; d = 0.61), absolute FM (p < 0.0001; d = 0.85), relative FM (p < 0.0001; d = 0.84), BMI (p = 0.0001; d = 0.60), WC (p < 0.0001; d = 0.92), HC (p = 0.003; d = 0.51) and WHR (p < 0.0001; d = 0.90) after 12 weeks. No significant differences were observed between groups or in interaction effects for these parameters. Both groups maintained LBM throughout the intervention. Adherence rates were significantly higher in TRE (5.78 ± 1.13 days/week) compared to VD (5.29 ± 1.49 days/week; p = 0.0002). Adherence declined over time in both groups but not significantly. Dietary analysis showed no significant differences in energy and macronutrient intake.

Conclusion: VD led to the same results as TRE but with a significantly lower adherence rate in the 12-week intervention period. Both dietary approaches reduced BW and FM and maintained LBM in middle-aged, physically active individuals without changing physical activity levels. Therefore, VD and TRE may counteract age-related body composition changes as long-term measures. Further studies with larger samples and a longer study duration are needed to confirm these findings.

Registration number: DRKS00033809.