Effects of Weight Change and Weight Cycling on Lung Function in Overweight and Obese Adults.

Rationale: Epidemiological studies have reported on the detrimental effects on lung function after natural, and thus limited, weight gain in unselected populations. Studies on bariatric surgery, on the contrary, have indicated large improvements in lung function after substantial weight loss. Objectives: To study the associations between profound weight loss or gain and pulmonary function within the same population. A second objective was to investigate the effect of weight cycling on pulmonary function. Methods: From our lung function database, we selected the records of subjects in follow-up for continuous positive airway pressure therapy for sleep apnea with a weight change of ⩾20 kg within 5 years. Lung function ( N  = 255) at baseline was normal except for a tendency toward mild restriction in morbid obesity. Within this sample, 73 subjects were identified with significant "weight cycling", defined as a ⩾10-kg opposite change in body weight before or after the ⩾20-kg weight change. Results: Weight change affected pulmonary function more in men than in women ( P  < 0.001). In men, forced vital capacity (FVC) increased an average of 1.4% predicted per unit of body mass index after weight loss and the reverse after weight gain, whereas women exhibited a smaller change of 0.9% predicted per unit of body mass index. Weight loss slightly increased the ratio of forced expiratory volume in 1 second to FVC and decreased the specific airway resistance, whereas the opposite occurred with weight gain. Greater effects of weight change on lung function were observed in leaner subjects ( P  = 0.02) and in older subjects ( P  < 0.002). Changes in total lung capacity followed the changes in FVC, with no change in residual volume, and the greatest change was observed in functional residual capacity. In subjects with weight cycling, the improvement in lung function due to weight loss was reversed by subsequent weight gain and vice versa. Conclusions: This study provides evidence that the detrimental effect of obesity on lung function is a passive and reversible process.