CPAP Effects on Energy Expenditure, Intake, Hormonal Regulation, and Body Composition: A Randomized Trial.

Study Objectives: Weight gain after continuous positive airway pressure (CPAP) initiation in obstructive sleep apnea (OSA) is common, but its mechanism and relevance remain unclear. This open-label randomized trial evaluated CPAP effects on energy expenditure, intake, body composition, physical activity, and appetite-regulatory hormones.

Methods: Patients with OSA were randomized (1:1) to 12-week CPAP or inactive control. The primary outcome was resting energy expenditure (REE). Secondary outcomes included dietary intake, eating behavior, fat mass (FM), fat-free mass (FFM), and activity count. Tertiary outcomes included appetite-regulatory hormones. CPAP effects were assessed as baseline-adjusted between-group differences using intention-to-treat (ITT) analysis; Per-protocol analysis (completers) served as sensitivity analysis.

Results: Of 52 randomized participants, 45 completed the study. In ITT analysis, CPAP had no effect on REE (8.6 kcal/day [95% CI: -51.5, 68.7]; P=0.774) or caloric intake (144.4 kcal/day [95% CI: -123.1, 411.9]; P=0.283). Although insignificant in morning, CPAP significantly increased evening body weight (P=0.017) and body mass index in morning and evening (P=0.040 and 0.030). CPAP also increased FFM, raised acylated ghrelin and insulin-like growth factor 1, and reduced cortisol and cognitive restraint. No changes were observed in macronutrient intake, FM, activity, insulin resistance, leptin, or neuropeptide Y. Per-protocol findings were similar.

Conclusions: CPAP-induced weight gain, probably primarily from FFM, occurred without measurable changes in REE, activity, or significant increases in caloric intake. Accompanying hormonal and behavioral changes suggest a subtle positive energy balance. This gain may not reflect adverse metabolic effects and support evaluating CPAP's metabolic impact through body composition, not weight alone.