The Influence of Body Composition and Lifestyle Factors on Resting Energy Expenditure and Its Role in Cardiometabolic Risk: A Cross-Sectional Study

In this study, we investigated the associations between lifestyle factors (diet, physical activity, sleep), body composition, and resting energy expenditure (REE) in a cohort of 80 healthy, non-obese adults aged 30–45 years. Using indi-rect calorimetry, accelerometers, and bioelectrical impedance analysis (BIA), we assessed REE, physical activity levels, sleep duration, and biochemical parame-ters to identify factors contributing to individual variations in REE and their potential role in modulating cardiometabolic risk. We found that fat-free mass (FFM) was the strongest predictor of REE, along with related metrics such as total body water, body cell mass, and muscle mass (p < 0.0001, adj. R² > 0.5). In univariable models, all physical activity intensities were significantly associated with REE, but only moderate physical activity (MPA) remained significant after adjusting for sex and FFM (β = 2.2 ± 1.0, p < 0.05, adj. R² = 0.589). Similarly, a positive association between HDL-C and REE persisted after adjustments (β = 5.0 ± 2.0 kcal/d, p < 0.05, adj. R² = 0.588). These direct links may be attributed to habitual, spontaneous physical activity, which generates post-exercise metabolic elevation and promotes adipose tissue brown-ing, resulting in favorable metabolic effects. Other biochemical and lifestyle factors, including HOMA-IR, insulin levels, tri-glycerides, and total energy intake, showed positive associations with REE in the crude model. However, these relationships diminished after adjustment, suggesting that their influence is likely mediated by factors such as body compo-sition, body size, and sex. Finally, no significant relationship between sleep and REE was observed in our cohort under naturalistic conditions, possibly due to the alignment of participants’ sleep durations with recommended guidelines.