Tracking and Changes in Diet, Body Composition, and Obesity from Childhood to Adolescence

This dissertation consists of three parts: (1) Dynamics of Body mass index (BMI) and its association with dietary intake; (2) Tracking patterns of overweight; and (3) Tracking of dietary patterns from childhood to adolescence. I studied over 1500 children, initially aged 6-13 and surveyed in the 1991, 1993, and 1997 China Health and Nutrition Surveys. Patterns of BMI maintenance (tracking) and changes in children's overweight status coexisted over a six-year period. About 40% maintained their relative position (quartile). Thin and fat children were more likely to track their initial BMI status: 51% and 46% remained in the bottom and top quartiles, respectively. Of the 95 overweight children in 1991, 37% remained overweight in 1993; fewer remained overweight during 1993-97 (16%) and 1991-97 (7%). Changes in children's energy intake and diet composition affected changes in BMI. Increased intakes of energy, meat, and fat promoted greater increase rates in BMI. Changes in energy intake were positively associated with changes in meat and fat intakes, but negatively related to vegetable and fruit (VF) and carbohydrate intakes. Children's baseline BMI, dietary intake, family income, and parental body weight status helped to predict tracking patterns of BMI. Compared to the "overweight non-tracking group" (overweight [implies] non-overweight), the "tracking group" (overweight [implies] overweight) had higher baseline fat intake, but lower carbohydrate intake. They were also more likely to have high-fat (% energy > 30%) and high-meat (top quartile) diets, but less likely to have high-carbohydrate (energy % > 70%) or high-VF (top quartile) diets. Tracking of fatness related to tracking of high-meat and high-fat diets. Children tracked dietary patterns over time. Correlations were 0.3-0.5 for macronutrient and major food group intakes. About half of those initially had high-fat, high-carbohydrate, high-VF, and high meat diets maintained such diets six years later. Socioeconomic status factors such as urban-rural residence, family income, parental education, and dietary intake at baseline were the important predictors. In conclusion, even under conditions of considerable socioeconomic changes, children track their BMI and dietary patterns. Energy intake affects BMI. The composition of diet (macronutrients and food groups) influences children's energy intake, and in turn, affects their BMI trajectory and risks for overweight.

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