Effect of Time-Restricted Eating on Metabolic Adaptation in Adults With Severe Obesity During Early Phase of Weight Loss

OBJECTIVE: To compare metabolic adaptations at the early phase of weight loss in individuals with severe obesity assigned to two strategies of energy restriction: continuous or in combination with time-restricted eating (TRE). METHODS: 100 participants (> 40 kg/m²; 20-60 years) were randomized into two groups: continuous energy restriction (CER, n = 42) and TRE combined with energy restriction (TRE + ER; eating window: 10am-6pm). Resting metabolic rate (RMR) by indirect calorimetry, body composition by dual-energy X-ray absorptiometry (DXA), serum hormones, and appetite feelings were evaluated at baseline and after 1 week of prescribed diet at 60% the total energy expenditure. Early adaptive thermogenesis (AT) was calculated using measured and predicted RMR. Data were evaluated using ANCOVA and linear mixed-effects model. RESULTS: After adjustment for RMR at baseline and body composition, RMR after 1 week was similar between groups (β_group = 47 ± 32 kcal/day; p = 0.148). Early AT was significantly lower in the TRE + ER group (-13 ± 160 kcal vs. -83 ± 150 kcal; p = 0.038). After a week of energy restriction, leptin, insulin, and TSH concentrations decreased in both groups (time effect, p < 0.05) with no group x time interaction. The feeling of hunger increased after 1 week only in the CER group (p = 0.048). CONCLUSION: Results suggest that TRE modestly attenuate early AT, but this effect does not translate into differences in RMR after 1 week. Hormonal and appetite responses were also not substantially affected by TRE. Further studies are needed to determine whether the modest early effects of TRE translate into clinically meaningful long-term benefits for weight management.