Predictors of body fat gain in nonobese girls with a familial predisposition to obesity.

BACKGROUND: Conflicting evidence exists on the causal factors underlying the development of excess adiposity in children.
OBJECTIVE: We determined the effect of energy expenditure (EE), muscle energetics, and physical fitness on weight and fat gain in prepubertal girls with or without a predisposition to obesity.
DESIGN: Normal-weight girls (n = 101) were recruited at 8 y of age according to parental body mass index. Eighty-eight girls completed the 2-y study, and the groups were as follows: LN, girls with 2 lean parents; LNOB, girls with 1 obese and 1 lean parent; and OB, girls with 2 obese parents. Measurements of weight, height, and body composition were taken 1 and 2 y after baseline. Girls underwent baseline measurements of EE by 24-h calorimetry and doubly labeled water, of muscle metabolism by (31)P nuclear magnetic resonance, and of fitness.
RESULTS: Fat mass (FM) and percentage body fat (%BF) differed significantly between the groups at years 1 and 2; the OB group had higher FM (P = 0.03) and %BF (P = 0.046) at year 1 and higher FM (P = 0.047) at year 2 than did the LN group. After adjustment for baseline weight, group, time, ethnicity, and Tanner stage, sleep EE, basal EE, 24-h EE, and peak oxygen uptake were negatively associated with FM and %BF (P < 0.04). After adjustment for the same variables, muscle oxidative capacity and free-living total EE were negatively and positively predictive, respectively, of changes in %BF between 8 and 10 y of age (both P = 0.04).
CONCLUSIONS: Nonobese girls with 2 obese parents have a significant risk of developing obesity. High free-living total EE and low muscle oxidative capacity predict high rates of fat gain.