Obesity has been recognized as a worldwide pandemic, and the first-line treatment is weight loss via a calorie restricted diet (1). Obstructive sleep apnea (OSA) is recognized as one of the key obesity-related comorbidities and has complex interactions with obesity and weight loss treatments. Treating OSA with continuous positive airway pressure (CPAP) is recommended widely in clinical practice as an adjunct therapy with weight loss despite a lack of evidence to support the strategy. Therefore, we conducted a retrospective study with the patients seen in UAMS weight loss clinic from 1/1/2014 to 8/31/2017. Patients were eligible if they were 18-65 years old, body mass index >= 30 and < 50, and underwent a 16-week intensive calorie restriction weight loss program obtained by strict calorie restriction (800 Kcal per day), exercise programs, weekly individual counseling and cognitive behavioral therapy. Patients who suffered from thyroid dysfunction, uncontrolled diabetes, active infection, active malignancy, or end-organ damage were excluded. Participants underwent a standardized medical examination before and every week in the program. Of the 300 patients included in the analysis, the average ages was 55 ± 10 years old, and 236 (78.7%) were female. They were divided into three groups based on self- reported OSA symptoms and CPAP treatment status: asymptomatic OSA group (OSA-A, n = 89), symptomatic group (OSA-S, n = 164), and OSA on CPAP treatment group (OSA-T, n = 47). In 16 weeks, the absolute weight loss of the OSA-T group was significantly higher than that of the OSA-S and OSA-A groups (-12.1 ± 5.9 vs. -9.5 ± 5.5 vs. -8.7 ± 5.3 kg, P < 0.01), whereas, the percentage weight loss of the OSA-T group was not significantly higher than that of the OSA-A and OSA-S groups (-10.46 ± 5.63% vs. -9.14 ± 4.89% vs. -8.47 ± 4.97%, P = 0.065). There had no difference of the absolute weight loss between OSA-A group and OSA-S group. Further analysis established a correlation of CPAP treatment to the absolute weight loss (Spearman’s correlation coefficient -0.181, P = 0.013) after adjustment of baseline body mass index, age and gender. Our results showed that the patients who had CPAP treatment achieved a larger weight reduction than non-CPAP treatment patients in a 16-week intensive calorie restriction weight loss program. Sleep quality may impact success in weight loss programs and several mechanisms may underpin this. Reference: (1) Varady KA. Intermittent versus daily calorie restriction: Which diet regimen is more effective for weight loss? Obes Rev. 2011;12:e593-e601.