Intake of amino acids by breast-milk-fed infants and amino acid composition of cow's milk and human milk

Abstract

Records of three infant girls' growth and nitrogen intake from their respective mothers' milk provide data upon the relationships between gain in body weight, volume intake of milk, concentration of protein in human milk, and estimated protein deposition in body tissue. The amino acid intakes from breast milk protein by two normal, healthy infant girls during the first five months of life and for a third infant girl during her fourth and fifth months of life have been estimated from amino acid analyses of human milk proteins. During their first five months, two infants of similar birth weight gained 3,260 and 3,220 Gm. of body weight, respectively, from 116.5 and 115.2 liters of their mothers' breast milk, containing 1,114 and 1,209 Gm. of protein. By Rubner's estimate of 30 Gm. of nitrogen per kilogram of body tissue, 611 and 604 Gm. of protein, respectively, were deposited in the infants' bodies, or approximately one-half of the protein intake. The third infant, who weighed approximately 800 Gm. less at birth, demonstrated equally satisfactory gains in body weight on less milk of greater protein concentration. Calculated from analyses of mature human milk, these two infants'intakes of seven amino acids during their second through fifth months of life were, respectively, 13 and 15 Gm. histidine, 42 and 50 Gm. arginine, 52 and 62 Gm. lysine, 52 and 62 Gm. tyrosine, 20 and 23 Gm. tryptophane, 21 and 25 Gm. cystine, and 19 and 23 Gm. methionine. A comparison has been made of the composition of cow's milk andhuman milk proteins with respect to seven amino acids, histidine, arginine, lysine, tyrosine, tryptophane, cystine, and methionine. Gram for gram of protein, the two milks are nearly equivalent in histidine, arginine, lysine, tyrosine, tryptophane, and organic sulfur; however, the organic sulfur in human milk protein is quite evenly divided between cystine and methionine, while in cow's milk protein the sulfur is largely in the form of methionine. A possible relationship between this difference in sulfur distribution and the relative nutritive value of the milks of the two species is discussed. Records of three infant girls' growth and nitrogen intake from their respective mothers' milk provide data upon the relationships between gain in body weight, volume intake of milk, concentration of protein in human milk, and estimated protein deposition in body tissue. The amino acid intakes from breast milk protein by two normal, healthy infant girls during the first five months of life and for a third infant girl during her fourth and fifth months of life have been estimated from amino acid analyses of human milk proteins. During their first five months, two infants of similar birth weight gained 3,260 and 3,220 Gm. of body weight, respectively, from 116.5 and 115.2 liters of their mothers' breast milk, containing 1,114 and 1,209 Gm. of protein. By Rubner's estimate of 30 Gm. of nitrogen per kilogram of body tissue, 611 and 604 Gm. of protein, respectively, were deposited in the infants' bodies, or approximately one-half of the protein intake. The third infant, who weighed approximately 800 Gm. less at birth, demonstrated equally satisfactory gains in body weight on less milk of greater protein concentration. Calculated from analyses of mature human milk, these two infants'intakes of seven amino acids during their second through fifth months of life were, respectively, 13 and 15 Gm. histidine, 42 and 50 Gm. arginine, 52 and 62 Gm. lysine, 52 and 62 Gm. tyrosine, 20 and 23 Gm. tryptophane, 21 and 25 Gm. cystine, and 19 and 23 Gm. methionine. A comparison has been made of the composition of cow's milk andhuman milk proteins with respect to seven amino acids, histidine, arginine, lysine, tyrosine, tryptophane, cystine, and methionine. Gram for gram of protein, the two milks are nearly equivalent in histidine, arginine, lysine, tyrosine, tryptophane, and organic sulfur; however, the organic sulfur in human milk protein is quite evenly divided between cystine and methionine, while in cow's milk protein the sulfur is largely in the form of methionine. A possible relationship between this difference in sulfur distribution and the relative nutritive value of the milks of the two species is discussed.