Free Amino Acids in Human Milk and Associations With Maternal Anthropometry and Infant Growth

Free glutamic acid has an appetite-regulating effect and studies with infant formula have suggested that free amino acids (FAA), especially glutamic acid, can downregulate intake. The content of glutamic acid and glutamine is high in breast milk but varies considerably between mothers. The aim was to investigate whether maternal anthropometry was associated with the content of the FAA glutamic acid or glutamine in breast milk and whether there was a negative association between these FAA and current size or early infant growth in fully breastfed infants.

From a subgroup of 78 mothers, of which 50 were fully breast feeding, from the Odense Child Cohort breast milk samples were collected 4 months after birth and analyzed for FAA. Information regarding breastfeeding status and infant weight and length was also recorded.

There was a large variation in the concentration of the FAAs between mothers. Glutamic acid was positively correlated with mother's prepregnancy weight and height (P ≤ 0.028), but not body mass index. There was no negative correlation between the 2 FAA and infant weight or body mass index. Infant length at 4 months was, however, positively associated with glutamine, (P = 0.013) but the correlation was attenuated when controlling for birth length (P = 0.089).

The hypothesis that a high content of glutamic acid and glutamine in breast milk could downregulate milk intake to a degree affecting early growth could not be confirmed. Maternal factors associated with the level of these FAA in milk and the potential effect on the infant should be investigated further.