Associations between self-reported and objectively measured physical activity, sedentary behavior and overweight/obesity in NHANES 2003-2006

OBJECTIVE: To investigate associations between self-reported and objectively measured physical activity, sedentary behavior and overweight/obesity based on percent body fat measured with Dual Energy X-Ray Absorptiometry (DXA), waist circumference (WC), waist-to-height ratio and body mass index, focusing on different intensities and domains of physical activity. METHODS: Data from NHANES 2003-2006 were analyzed using linear and ordered logistic regression analyses. A total of 4794 individuals aged 18-69 years with valid physical activity and DXA data were included. Objectively measured physical activity and sedentary behavior were assessed using accelerometers, self-reported physical activity using the NHANES physical activity questionnaire. Weight, height, WC and DXA measures were assessed in the mobile examination centers. RESULTS: We observed statistically significant associations between objectively measured moderate and vigorous physical activity and all definitions of overweight/obesity. For total physical activity, the odds of being in the higher percent body fat category were 0.56 (95% confidence interval (CI) 0.41, 0.77) for the medium and 0.30 (95% CI 0.22, 0.40) for the highest physical activity tertile compared with the lowest. For light activities, lifestyle activities and sedentary behavior, associations were only observed in the linear models with percent total body fat but not in the ordered logistic regression models. Regarding self-reported physical activity, consistent significant associations with overweight/obesity were only observed for vigorous and for transport activity. CONCLUSIONS: Regarding moderate and vigorous physical activity, more active individuals were less affected by overweight/ obesity than less active individuals, emphasizing the public health effect of physical activity in the prevention of overweight/ obesity. The fact that associations were more consistent for objectively measured than for self-reported physical activity may be due to bias related to self-reporting. Associations between lower intensity activities and overweight/obesity were weak or inexistent.