Glutamate Supply and Metabolism in Infants

Glutamate (Glu) is the most abundant amino acid (AA) in human milk. Available information on Glu supply and metabolism was reviewed, based on an electronic literature search. In 22 cross-sectional global studies with 4,747 women, free Glu increases with lactation duration and contributes to about 38% of total and 63% of dispensable milk AA. Based on these data, a typical breastfed infant obtains a mean free Glu intake of 35.7 mg/kg body weight (bw; upper end of the normal range 134.6 mg/kg), while precisely collected longitudinal data indicate mean intakes of 40 mg/kg and upper range intakes of 70.2 mg/kg. Mean intakes with cows' milk formula at median concentrations are 0.7 mg/kg (upper range 1.0 mg/kg) and with extensive protein hydrolysate formula 171.7 mg/kg bw (upper range 249.8 mg/kg bw), with no indication of untoward effects. Infants almost entirely utilize dietary Glu in splanchnic organs, with no appreciable effect on plasma Glu concentrations. Estimated free Glu intakes in breastfed infants are up to 4.5-fold higher than the acceptable daily intake (ADI) set by the European Food Safety Authority for the total population including infants, and the respective intakes of infants fed a formula based on an extensive protein hydrolysate are up to 8.3-fold higher. There is no reason to assume that feeding human milk or an extensive protein hydrolysate infant formula would be unsuitable or unsafe for infants. Setting an ADI below the range of the normal intake with a safe diet in generally healthy individuals, that is, below 250 mg/kg per day, seems inappropriate.