Physical Activity Improves Glucose Tolerance Independent of Weight Loss in Severe Obesity

Background: Impaired glucose tolerance, a risk factor for the development of type 2 diabetes, has a very high prevalence in obese subjects. This study aims to explore the contributions of changes in weight, physical activity (PA), sleep efficiency (SE) and excessive daytime sleepiness (EDS) to changes in glucose tolerance in severely obese subjects during a commercial lifestyle modification programme. Methods: At intake, after 3 and 6 months of treatment, 33 subjects (28.2% male, age: 42.7 +/- 12.3 years, weight: 118.1 +/- 23.8, BMI: 40.0 +/- 7.3 kg/m(2)) were subjected to an oral glucose tolerance test (OGTT), wore an accelerometer for 6 consecutive days and weight and body composition were measured. Results: After 6 months of treatment there was a significant reduction in weight -11.1 kg, BMI -3.8 kg/m(2), waist circumference -10.8 cm, % Body fat -4.7% and fat mass -10.2 kg (all values p at least <0.001). Glucose tolerance (2 h glucose during OGTT) (0.8 mmol/L, p=0.042) showed a significant improvement. PA, SE and EDS did not change significantly. Changes in weight and PA contributed significantly to the change in glucose tolerance (weight 16%, p=0.021; PA 11%, p=0.049). Conclusion: We conclude that this commercial lifestyle modification programme significantly reduced weight, waist circumference, % body fat and fat mass and improved glucose tolerance after 3 and 6 months of treatment. The improvement in glucose tolerance was partly explained by the changes in weight and PA, but not by SE or EDS. This study reveals that severely obese subjects benefit from an increase in physical activity independent of weight loss with regard to improvements in glucose tolerance.