High protein intake in infancy might lead to a higher body mass index (BMI) in childhood. However, whether these associations differ between different sources of protein is unclear.We investigated associations between the intake of total protein, protein from different sources, and individual amino acids in early childhood and repeatedly measured height, weight, and BMI up to the age of 9 y.This study was performed in 3564 children participating in the Generation R Study, a population-based prospective cohort study in Rotterdam, Netherlands. Intakes of total protein, animal protein, vegetable protein, and individual amino acids (including methionine, arginine, lysine, threonine, valine, leucine, isoleucine, phenylalanine, tryptophan, histidine, cysteine, tyrosine, alanine, asparagine, glutamine, glycine, proline, and serine) at 1 y were assessed by using a food-frequency questionnaire. Height and weight were measured at the approximate ages of 14, 18, 24, 30, 36, and 45 mo and at 6 and 9 y, and BMI was calculated.After adjustment for confounders, linear mixed models showed that a 10-g higher total protein intake/d at 1 y was significantly associated with a 0.03-SD greater height (95% CI: 0.00, 0.06), a 0.06-SD higher weight (95% CI: 0.03, 0.09), and a 0.05-SD higher BMI (95% CI: 0.03, 0.08) up to the age of 9 y. Associations were stronger for animal than for vegetable protein intake but did not differ between dairy and nondairy animal protein or between specific amino acids.A higher intake of protein, especially animal protein, at 1 y of age was associated with a greater height, weight, and BMI in childhood up to 9 y of age. Future studies should explore the role of growth hormones and investigate whether protein intake in early childhood affects health later in life.

Dietary Intake of Protein in Early Childhood Is Associated with Growth Trajectories between 1 and 9 Years of Age