High birth weight predicts subsequent obesity, but paradoxically, a reduced risk of subsequent cardiovascular disease compared with low birth weight. This apparent paradox might be explained if high birth weight programmed a greater proportion of subsequent lean mass, which carries less cardiovascular risk than fat tissue.
The aim of this study was to test the hypothesis that the direct correlation between birth weight and subsequent body mass index (BMI) represents an association between birth weight and lean tissue, and to assess the metabolic impact of this relationship.
A total of 234 healthy prepubertal children (133 boys, 101 girls, mean age 5.9 yr +/- 0.3 standard deviation) were studied. Birth weights were obtained from maternity records. Lean mass was measured by bioelectrical impedance. Anthropometric measures included height, weight (BMI), waist circumference, and subcutaneous fat mass (FM). Insulin resistance was assessed by the homeostasis model method. Metabolic correlates of insulin resistance included total and high-density lipoprotein cholesterol, triglycerides, and sex-hormone-binding globulin.
Birth weight correlated significantly with lean mass in boys (r = 0.41, p < 0.001) and girls (r = 0.27, p < 0.01). Adjusting for BMI did not improve the correlation further. After adjustment for FM, lean mass correlated inversely with triglycerides in boys only (r = -0.41, p < 0.01). Birth weight correlated inversely with triglycerides in boys (r = -0.18, p < 0.05); after adjustment for lean mass, this correlation was not significant.
In boys, the relationships between birth weight, triglycerides, and lean mass are consistent with the hypothesis. Overall, our findings provide limited evidence in support of the argument that higher birth weight predicts lower metabolic risk because it marks programming of more lean mass.