Changes in fat mass and fat-free mass during the adiposity rebound: FLAME study

To prospectively examine the relation between television watching and body fat change in children from preschool to early adolescence. In a longitudinal study, 106 children were enrolled during preschool years (mean age 4.0 y) and followed into early adolescence (mean age 11.1 y). Parents completed an annual questionnaire on the child's television and video habits. Body mass index (BMI), triceps skinfolds, and sum of five skinfolds were recorded yearly at annual clinic visits. Longitudinal statistical analyses were carried out using mixed modeling procedures to control for potential confounding by a number of factors. Television watching was an independent predictor of the change in the child's BMI, triceps, and sum of five skinfolds throughout childhood. Its effect was only slightly attenuated by controlling for the baseline body fat, level of physical activity (as measured repeatedly by Caltrac accelerometer), percent of calories from fat, total calorie intake, or the parents' BMI or education. By age 11, children who watched 3.0 h or more of television per day had a mean sum of skinfolds of 106.2 mm, compared with a mean sum of skinfolds of 76.5 mm for those who watched less than 1.75 h per day (P=0.007). Furthermore, the adverse effect of television viewing was worse for those children who were also sedentary or had a higher-fat diet. Children who watched the most television during childhood had the greatest increase in body fat over time. Healthy lifestyle education designed to prevent obesity and its consequences should target television-watching habits of children.

Declining levels of physical activity in the population at large may be responsible in part for the rising rates of childhood obesity. Studies to date, however, have not consistently demonstrated such a protective effect. We used longitudinal data from the Framingham Children's Study (FCS) to address this important question. We used 8 years of activity monitoring (Caltrac electronic motion sensors) and repeated anthropometry measures for 103 children to examine the effect of activity on body fat change from preschool to early adolescence. Longitudinal data analysis methods were employed to account for the use of repeated measures on these children. Children in the highest tertile of average daily activity from ages 4 to 11 years had consistently smaller gains in BMI, triceps, and sum of five skinfolds throughout childhood. By early adolescence (age 11), the sum of five skinfolds was 95.1, 94.5, and 74.1 for the low, middle, and high tertiles of activity, respectively (P for trend = 0.045). This protective effect of activity was evident for both girls and boys. This longitudinal study adds strong support for the hypothesis that higher levels of physical activity during childhood lead to the acquisition of less body fat by the time of early adolescence.

Understanding the determinants of adiposity in young children may be particularly critical for preventing adult obesity since the age at which body fatness reaches a postinfancy low point (typically 4-6 years) is inversely associated with obesity later in life. METHODS; We examined cross-sectional associations among fatness, leanness, and physical activity in 467 children (range 4-6 years). Activity was measured using accelerometry and parental report of children's television (TV) viewing. Dual energy X-ray absorptiometry was used to quantify body composition. Minutes spent in vigorous activity and TV viewing were the variables most consistently and most highly associated with adiposity. Children in the lowest quartile for vigorous activity had on average (absolute) body fat percentages that were 4% greater than those children in the highest quartile for vigorous activity. Body fat percentages for children in the highest category for TV viewing were on average 3% greater than those children who watched the least amount of TV. Low levels of vigorous physical activity and high levels of TV viewing are associated with fatness in young children during the adiposity rebound period. This suggests that increasing children's active play may be important in preventing obesity later in life.