Introduction: Higher protein intake during the first year of life is associated with increased weight gain velocity and body mass index (BMI). However, the relationship of protein intake and weight gain velocity with body composition is unclear.
Objective: To assess if the increases in weight gain velocity and BMI induced by protein intake early in life are related to an increase in fat or fat-free mass.
Materials and methods: In all, 41 infants randomized at birth to a higher or lower protein content formula (HP=17 and LP=24, respectively) and 25 breastfed infants were included. Anthropometric measures were assessed at baseline, 6, 12 and 24 months, and fat-free mass (FFM) and fat mass (FM) were assessed by isotope dilution at 6 months.
Results: Weight gain velocity (g per month) during the first 6 months of life was significantly higher among HP infants (807.8 (±93.8) vs 724.2 (±110.0) (P=0.015)). Weight gain velocity strongly correlated with FM z-score (r=0.564, P<0.001) but showed no association with FFM z-scores. FFM showed no association with BMI. Nevertheless, FM strongly correlated with BMI at 6, 12 and 24 months (r=0.475, P<0.001; r=0.332, P=0.007 and r=0.247, P=0.051, respectively). FFM and FM z-scores did not differ significantly between HP and LP infants (0.32±1.75 vs -0.31±1.17 and 0.54±2.81 vs -0.02±1.65, respectively).
Conclusion: Our findings support the hypothesis that higher protein intakes early in life are associated with faster weight gain and in turn to higher adiposity. This mechanism could be a determinant factor for later obesity risk.