Assessing Risk Factors for Obesity Between Childhood and Adolescence: II. Energy Metabolism and Physical Activity

OBJECTIVE: To assess the effect of energy expenditure, including resting metabolic rate (RMR), total energy expenditure (TEE), and activity energy expenditure (AEE), as well as substrate oxidation (respiratory quotient RQ), on the development of obesity in a large cohort of Native American children with a high propensity for obesity. METHODS: During the summer months of 1992 to 1995 and again 5 years later, 138 (65 boys and 73 girls) 5-year-old Pima Indian children were studied. At baseline and follow-up, height and weight were measured; body composition was assessed with the use of 18O dilution; RMR and RQ were assessed with the use of indirect calorimetry; TEE was measured with the use of the doubly-labeled water method; and AEE was calculated (TEE - RMR + 0.1 x TEE). In addition, an activity questionnaire was used to assess participation in sporting activities as well as television viewing during the previous year. Linear regression models were used to assess the effects of the baseline variables on the development of obesity. RESULTS: Pima Indian children were markedly overweight at both 5 and 10 years of age. Cross-sectionally, percentage of body fat and body weight at 5 and 10 years of age were negatively correlated with sports participation and positively correlated with television viewing. Most important, there was a marked change in the correlation between body size and activity between 5 and 10 years of age: at age 5 years, weight was positively correlated with AEE and PAL, but at age 10 years, the correlation with AEE was lost and that with PAL was negative. However, prospectively, none of the variables measured at baseline was a predictor of percentage of body fat at age 10 years after adjustment for percentage of body fat at age 5 years. CONCLUSIONS: At age 5 years, obesity is associated with decreased participation in sports and increased television viewing but not with a decreased PAL. At age 10 years, obesity is associated with decreased participation in sports, increased television viewing, and a decreased PAL, suggesting that a decrease in PAL in free-living conditions seems to follow, not precede, the development of obesity.