Time-restricted eating modestly attenuates early adaptive thermogenesis in severe obesity, but RMR and hormones remain similar to continuous restriction.

Achieving sustainable weight loss in individuals with severe obesity is challenging, often complicated by metabolic adaptation which can hinder progress and promote weight regain. A key aspect of this adaptation is a reduction in resting metabolic rate (RMR), known as adaptive thermogenesis (AT), which occurs in response to energy restriction. Current weight loss strategies frequently encounter plateaus due to this metabolic slowdown and increased appetite. Time-restricted eating (TRE) has emerged as a potential strategy to mitigate these adverse metabolic adaptations and improve adherence, but its specific impact on early AT and hormonal responses in severe obesity remains underexplored.

This randomized controlled trial enrolled 100 participants with severe obesity (>40 kg/m², 20-60 years old). Participants were assigned to two groups: continuous energy restriction (CER) (n=42) or time-restricted eating (TRE) combined with energy restriction (TRE+ER). The TRE+ER group maintained an eating window from 10 am to 6 pm. Both groups followed a prescribed diet providing 60% of their total energy expenditure for 1 week. Researchers evaluated resting metabolic rate (RMR) via indirect calorimetry, body composition using dual-energy X-ray absorptiometry (DXA), serum hormones (leptin, insulin, TSH), and subjective appetite feelings at baseline and after the 1-week intervention. Early adaptive thermogenesis (AT) was calculated by comparing measured and predicted RMR.

After 1 week of energy restriction, the resting metabolic rate (RMR) was similar between the groups, even after adjusting for baseline RMR and body composition (β_group = 47 ± 32 kcal/day; p=0.148). However, early adaptive thermogenesis (AT) was significantly lower in the TRE+ER group. > The TRE+ER group experienced an AT of -13 ± 160 kcal, compared to -83 ± 150 kcal in the CER group, indicating a 70 kcal attenuation of AT (p=0.038). Serum concentrations of leptin, insulin, and TSH decreased significantly in both groups after 1 week of energy restriction (time effect, p<0.05), with no significant group x time interaction observed. Interestingly, the feeling of hunger increased after 1 week only in the CER group (p=0.048), suggesting a potential benefit of TRE on appetite regulation in the short term.