Physical Activity Impacts Insulin Sensitivity Post-Metabolic Bariatric Surgery in Adolescents with Severe Obesity

BACKGROUND/OBJECTIVES: We hypothesized that physical activity (PA) improves insulin sensitivity in adolescents with severe obesity beyond that attributable to metabolic bariatric surgery (MBS). SUBJECTS/METHODS: StepWatch™ monitors objectively measured PA in 88 participants in the Teen Longitudinal Assessment of Bariatric Surgery (Teen-LABS) study. Primary outcomes included absolute change in fasting insulin, HOMA-IR, and fasting glucose from pre-surgery (baseline) to 6, 12, 24, and 36 months post-MBS. SAS PROC TRAJ generated activity trajectories based on probability and individual participant step count trajectories. Linear regression models were used, adjusted for baseline value, visit, surgical procedure, sex, and percent change in BMI. Additional models adjusted for percent change in iliac waist circumference (IWC) or percent body fat (BF), measured by bio-impedance. RESULTS: Two activity trajectories were identified: more active (MA, n=13) and less active (LA, n=75). MA baseline mean daily step count was >6 000, increasing to > 9 000 at 2 years. LA mean daily step count remained at approximately 4 000. Few participants recorded moderate step activity (cadence >80 steps/minute). Still, fasting insulin and HOMA-IR differed in association with activity trajectory. MA was associated with a greater absolute decrease in fasting insulin (−7.8μU/ml [95% CI: (−11.8, −3.7)], p =<0.001) and a greater decrease in HOMA- IR (−1.9 [95% CI: (−3.0, −0.7)], p = 0.001), when adjusted for percent change in BMI. The significant independent effect of MA remained when adjusted for percent change in IWC or percent BF. Clinically, 100% of MA trajectory participants normalized fasting insulin, HOMA-IR and fasting glucose by 6 months and normalization remained throughout the 36 month follow up. In contrast, 76.3% and 65.8% of LA trajectory participants normalized fasting insulin and HOMA-IR, respectively, by 12 months with 28.6% of both remaining normalized at 36 months. CONCLUSION: PA is independently associated with improved insulin sensitivity beyond that attributable to MBS in adolescents with severe obesity.