Continuous positive airway pressure (CPAP) therapy was associated with weight gain at two years in a cohort of predominantly older male patients with obstructive sleep apnea (OSA), in research conducted by investigators at Baylor College of Medicine in Houston. They reported their findings at CHEST 2011, the 77th annual meeting of the American College of Chest Physicians, in Honolulu. As known, obesity is causally linked to OSA. Weight change following treatment with CPAP is not clear. Although hormonal changes would predict weight loss, decreasing energy expenditure (EE) by reducing work of breathing would predict weight gain. Amarbir Mattewal, MD, and colleagues conducted a retrospective chart review of a clinical cohort of veterans diagnosed with OSA and treated with CPAP from January to May 2005. They defined OSA as apnea hypopnea index 5 (Medicare definition) and reviewed the electronic medical record for baseline data, sleep apnea severity, weight, blood pressure (BP), and blood glucose (BG) before and after starting CPAP. The exclusion criteria included prior CPAP treatment, central sleep apnea, head and neck deformity, immunosuppression, malignancy, and bariatric surgery. The investigators also determined changes in weight, BP, and BG over a three-year period after initiating CPAP treatment. A total of 61 patients (58 males, 3 females) met inclusion criteria. Their mean age was 63.8 years; mean weight at the time of study was 114 kg (251.3 lb). The mean weights at six months, one year, two years, and three years after CPAP initiation were 115.6 kg (254.8 lb), 115.7 kg (255.0 lb), 116.6 kg (257.0 lb), and 117.3 kg (258.6 lb), respectively. There was a trend towards weight gain at one year (P=0.06) after CPAP initiation and a statistically significant weight gain at two years compared to baseline (P=0.02). Sixty-four percent of patients gained a mean of 4.9 kg (10.8 lb).