Elevated weight contributes to obstructive sleep apnea (OSA). Some studies even suggest that OSA can contribute to elevated weight. Many of my patients know this and hope that they may lose weight by treating their OSA. This study is part of a larger one that examined the effect of CPAP therapy on neurocognitive functioning in patients with OSA. CPAP usage was monitored by the CPAP device - so the researchers knew if the patient was actually using CPAP enough. The researchers randomly assigned participants to either real CPAP or sham (fake) CPAP. The results showed that participants on real CPAP gained weight over six months, whereas those on the sham CPAP lost weight over the same time period. And interestingly, weight gain was greater the more the participant used the real CPAP per night. This effect was not seen in those on the sham CPAP. Finally, the results were independent of age, gender, race, OSA severity, and sleepiness.
Keep in mind that we are talking about small changes in weight - The real CPAP users, on average, gained less than one pound at the six month mark. And the sham CPAP users, on average, lost about 1.5 pounds during the same six months. The study authors do not know the reason for the weight increase in real CPAP users. They postulated that perhaps people with OSA burn more calories when they sleep due to the effects of stopping breathing - and that treating the OSA with real CPAP can mitigate that effect. I'm not sure I buy that argument. More studies will certainly be needed.
Bottom line - CPAP therapy is not a weight loss treatment - if it were, compliance would be much better and I would have a line of people outside my office wanting to get CPAP. But adherence to CPAP therapy is low and CPAP won't make people lose weight. Weight loss is achieved only with dietary change and exercise.