Changes in Energy Metabolism after Continuous Positive Airway Pressure for Obstructive Sleep Apnea

Rationale: Disrupted energy homeostasis in obstructive sleep apnea (OSA) may lead to weight gain. Paradoxically, treating OSA with continuous positive airway pressure (CPAP) may also promote weight gain, although the underlying mechanism remains unclear. Objectives: To explore the underlying mechanism by which patients with OSA gain weight after CPAP. Methods: A comprehensive assessment of energy metabolism was performed in 63 newly diagnosed OSA study participants (51 men; 60.8 +/- 10.1 yr; apnea-hypopnea index >20 h(-1)) at baseline, CPAP initiation, and at a 3-month follow-up. Measurements included polysomnography, body weight, body composition, basal metabolic rate (BMR), hormones (norepinephrine, cortisol, leptin, ghrelin, insulin-like growth factor-1), dietary intake, eating behavior, and physical activity. Measurements and Main Results: BMR significantly decreased after CPAP (1,584 kcal/d at baseline, 1,561 kcal/d at CPAP initiation, and 1,508 kcal/d at follow-up; P < 0.001), whereas physical activity and total caloric intake did not significantly change. In multivariate regression, baseline apnea-hypopnea index, Delta urine norepinephrine, and CPAP adherence were significant predictors of Delta BMR. The weight gainers had higher leptin levels, lower ghrelin levels, and higher eating behavior scores than the non-weight gainers, indicating a positive energy balance and disordered eating behavior among the weight gainers. Among the parameters related to energy metabolism, increased caloric intake was a particularly significant predictor of weight gain. Conclusions: Although a reduction in BMR after CPAP predisposes to a positive energy balance, dietary intake and eating behavior had greater impacts on weight change. These findings highlight the importance of lifestyle modifications combined with CPAP.