Physical Activity and 3-Year BMI Change in Overweight and Obese Children

OBJECTIVES: Targeting physical activity (PA) is a mainstay in obesity treatment, but its BMI benefits are poorly quantified. We studied longterm predictive PA-BMI relationships in overweight/obese children presenting to primary care. METHODS: Three-year follow-up of 182 overweight/obese 5to 10-yearolds recruited from 45 Melbourne general practices. Predictor: 7-day accelerometry (counts per minute, cpm). Outcomes: change in BMI z score, BMI category, and clinically significant BMI improvement (z score change $0.5). Analysis: Linear and logistic regression. RESULTS: Mean (SD) baseline and 3-year BMI z scores were 1.8 (0.6) and 1.8 (0.7), and mean (SD) activity scores 334 (111) and 284 (104) cpm, respectively. Baseline activity did not predict BMI change. However, for every 100 cpm increase in change in activity over 3 years, BMI z score fell by 0.11 (95% confidence interval [CI] 0.03–0.20; P = .006). There were also trends toward greater odds of staying in the same, versus moving to a higher, BMI category (odds ratio 1.85, 95% CI 0.99–3.46) and clinically significant BMI improvement (odds ratio 1.96, 95% CI 0.90–4.27; P = .09). Change in percentage time spent in moderate-vigorous (P = .01), but not sedentary (P = .39) or light (P = .59), activity predicted reduced BMI z score. CONCLUSIONS: Sustained increase in moderate-vigorous PA predicts reducing BMI z score over 3 years in overweight/obese children presenting to primary care. However, the small BMI change associated with even the largest activity changes may explain disappointing BMI outcomes of brief primary care interventions targeting PA. Pediatrics 2013;131:e470–e477 AUTHORS: Andrew Trinh, MBBS,ab Michele Campbell, PhD,ac Obioha C. Ukoumunne, PhD,d Bibi Gerner, MPsych,a,c and Melissa Wake, FRACP, MDabc aCentre for Community Child Health, Royal Children’s Hospital Parkville, and cMurdoch Childrens Research Institute, Parkville, Australia; bDepartment of Paediatrics, University of Melbourne, Parkville, Australia; and dPenCLAHRC, Peninsula College of Medicine and Dentistry, University of Exeter, Exeter, United Kingdom