The relationship of height and body fat to gender-assortative weight gain in children. A longitudinal cohort study (EarlyBird 44).

OBJECTIVE: Height, body fat and body mass index (BMI) are correlated in children, so we hypothesized that the gender-assortative associations in BMI recently reported in contemporary children might extend to their height and body fat. DESIGN: Prospective longitudinal cohort study. SUBJECTS: A total of 226 healthy trios (mother, father and child) from a 1995?1996 birth cohort randomly recruited in the city of Plymouth, UK. MEASUREMENTS: Height, weight, and BMI (kg/m(2)) were measured in each of the parents and, in addition, sum of five skin-folds (SF) in their children at 5, 6, 7 and 8 y. RESULTS: BMI and SF were strongly height-dependent in the children by 8 y (r = 0.41-0.56). SF was gender-assortative insofar as the mean SF was significantly greater in the daughters (but not the sons) of obese mothers (obese vs. normal weight: +2.5 cm p < 0.001) and in the sons (but not the daughters) of obese fathers (obese vs. normal: +1.3 cm p < 0.001). As expected, offspring height correlated with that of their parents, but overweight/obese children were systematically taller than normal weight children (boys: +1.02 SDS, girls: +1.14 SDS, p < 0.01), and this difference was independent of parental height or BMI. CONCLUSIONS: Height is transmitted by both parents, and the body fat of overweight/obese children largely by the same-sex parent, but the extra height associated with more fat in the child is unrelated to the height or weight of either parent. The secular trend in height among contemporary children may simply reflect their rising body fat. Excess fat is unhealthy, so the trend in height may not be healthy either.