The stability of children's weight status over time, and the role of television, physical activity, and diet.

Weight-related behaviors such as sedentary activity, physical activity, and diet have been the focus of efforts to prevent and reduce the occurrence of obesity and overweight in children, but few longitudinal studies have examined the effects of weight-related behaviors on changes in weight status over time in children. This study examines the effects of weight-related behaviors on subsequent changes in weight during childhood. We used the Early Childhood Longitudinal Study Kindergarten Cohort (ECLS-K), a nationally representative prospective cohort of children in the United States. Data, including anthropometric measures, were collected six times across 1998-2007 (analytic sample=4938). We employed an autoregressive cross-lagged model in a structural equation model framework to assess the effects of behavioral factors -intake of fruit, vegetables, fast food and sugar-sweetened beverages, television viewing, and physical activity - on weight stability over time. BMI z-scores were highly stable throughout childhood: the standardized parameter estimates of BMI z-scores on subsequent-period BMI z-scores ranged from 0.79 to 0.86. BMI z-scores were least stable between Kindergarten and 1st grade but became highly stable between 3rd and 5th grades. After accounting for prior weight, behavioral factors had little effect on subsequent weight. The most important behavioral factor was TV viewing in the 1st and 3rd grades: an additional hour of daily TV viewing was associated with 0.04 higher BMI z-score. It is important to prevent excessive weight gain early in childhood, as weight patterns are long-lasting; the most important behavioral factor may be limiting children's screen time.