Body Composition in Young Ethiopian Infants: Role of Birth Weight and Growth Velocity

Background Fetal and post-natal weight gain have been associated with both early survival and risk of later chronic disease in low-income populations, but the underlying early-life changes in body composition (BC) have not been described.

Objective To examine role of fetal and postnatal weight gain  as predictors for body composition at 6 months of age.

Subject and methods Prospective cohort study with repeated measurements of body composition using air- displacement plethysmography on 255 Ethiopian infants measured at 0, 6, 10, 14, 18 and 26 weeks of age. Fetal weight gain was indexed by birth weight, and infant weight gain by 6 months weight conditional on birth weight (conditional growth).

Results Low birth weight (the lowest birth weight tertile in the cohort) babies had less fat mass (FM) and fat-free mass (FFM) at birth. If they grew slowly they maintained a deficit at 6 months (FFMI deficit compared to reference group: -0.70, 95%CI: -1.21; -0.18, p=<0.01). If they grew fast they resolved the FFM deficit by 6 months, at a cost of greater fatness (FMI surplus compared to reference group: 1.18, 95%CI: 0.64; 1.72, p<0.01). There was a dose-response association, independent of birth weight, between post-natal weight gain and fatness at 6 months.

Conclusions Low birth weight babies have less FFM at birth. They can partially resolve this deficit by rapid post-natal weight gain, but at a cost of increased fat accretion. These findings show how prenatal and postnatal weight gain interacts to account for variability in infant body composition by 6 months. The longer-term consequences of these growth patterns for adult chronic disease risk remain unknown.