Threonine kinetics in preterm infants fed their mothers' milk or formula with various ratios of whey to casein. Infant regulation of intake: the effect of free glutamate content in infant formulas. Marginal dietary protein restriction reduced nonprotein nitrogen, but not protein nitrogen, components of human milk. Milk protein quantity and quality in low-birth-weight infants: II. Effects on selected aliphatic amino acids in plasma and urine.
BACKGROUND Plasma threonine concentrations are elevated in infants fed formula containing a whey-to-casein protein ratio of 60:40 compared with concentrations in infants fed formula containing a ratio of 20:80 or human milk ( 60:40 ) . OBJECTIVE We studied whether degradation of excess threonine was lower in formula-fed infants than in infants fed their mothers ' milk . DESIGN Threonine kinetics were examined in 17 preterm infants ( gestational age : 31+/-2 wk : birth weight : 1720+/-330 g ) by using an 18-h oral infusion of [1 - 13C]threonine at a postnatal age of 21+/-11 d and weight of 1971+/-270 g. Five infants received breast milk . Formula-fed infants ( n = 12 ) were r and omly assigned to receive 1 of 3 formulas ( 5.3 g protein/MJ ) that differed only in the whey-to-casein ratio ( 20:80 , 40:60 , and 60:40 ) . RESULTS Threonine intake increased significantly in formula-fed infants with increasing whey content of the formula ( 48.5 , 56.4 , and 63.2 micromol.kg(-1).h(-1 ) , respectively ; pooled SD : 2.2 ; P = 0.0001 ) , as did plasma threonine concentrations ( 228 , 344 , and 419 micromol/L , respectively ; pooled SD : 75 ; P = 0.03 ) . Despite a generous threonine intake by infants fed breast milk ( 58.0+/-16.0 micromol.kg(-1).h(-1 ) , plasma threonine concentrations remained low ( 208+/-41 micromol/L ) . Fecal threonine excretion and net threonine tissue gain , estimated by nitrogen balance , did not differ significantly among groups . Threonine oxidation did not differ significantly among formula-fed infants but was significantly lower in formula-fed infants fed than in infants fed breast milk ( 17.1 % compared with 24.3 % of threonine intake , respectively ) . CONCLUSION Formula-fed infants have a lower capacity to oxidize threonine than do infants fed breast milk BACKGROUND We recently discovered that infants r and omly assigned to a formula high in free amino acids ( extensive protein hydrolysate formula ; ePHF )  during infancy consumed less formula to satiation and gained less weight than did infants fed an isocaloric formula low in free amino acids ( cow milk formula ; CMF ) . OBJECTIVE Because ePHF and CMF differ markedly in concentrations of free glutamate , we tested the hypothesis that the higher glutamate concentrations in ePHF promote satiation and satiety . DESIGN In this counterbalanced , within-subject study , infants < 4 mo of age ( n = 30 ) visited our laboratory for 3 sets of 2 consecutive infant-led formula meals over 3 test days . Infants were fed 1 of 3 isocaloric formulas during each first meal : CMF , ePHF , or CMF with added free glutamate to approximate concentrations in ePHF ( CMF+glu ) . When infants signaled hunger again , they were fed a second meal of CMF . From these data , we calculated satiety ratios for each of the 3 formulas by dividing the intermeal interval by the amount of formula consumed during that particular first meal . RESULTS Infants consumed significantly less  CMF+glu  ( P < 0.02 ) and  ePHF  ( P < 0.04 ) than CMF during the first meals . They also showed greater levels of satiety after consuming CMF+glu  or ePHF : satiety ratios for CMF+glu ( P < 0.03 ) and ePHF ( P < 0.05 ) were significantly higher than for CMF . CONCLUSION These findings suggest a role of free glutamate in infant intake regulation and call into question the cl aim that formula feeding impairs infants ' abilities to self regulate energy intake OBJECTIVE This study was design ed to determine whether marginal dietary protein intakes of lactating women alter their milk production and composition . The study followed the observation that marginal dietary protein intakes lead to significantly negative nitrogen balances in these women . METHODS Twenty-four healthy , mature lactating women were divided evenly into three groups on the basis of postpartum times ; 1 , 5 , or 12 months . Each woman was given a controlled protein diet of either 1.5 ( HP ) or 1.0 ( MP ) g/kg body weight/day for 7 to 10 days . Milk production was measured for 72 hours by test weighing the infant before and after feeding . Milk sample s from alternate breasts were collected for 24 hours , pooled , and analyzed for their protein nitrogen , nonprotein nitrogen , free and protein-bound amino acid , and lactoferrin concentrations . RESULTS Reduced dietary protein intakes were associated with a decrease ( p < 0.05 ) in the nonprotein nitrogen and total free amino acid fractions of milk . Although urea was unaffected , the concentrations of milk free leucine , phenylalanine , histidine , and ornithine were lower ( p < 0.05 ) in the MP than in the HP group , while the output of leucine and histidine tended to be lower in the MP group . The amount of milk produced , as well as the amounts of protein nitrogen , protein-bound amino acid , and lactoferrin and their concentrations were unaffected by a reduction of dietary protein . CONCLUSIONS Maternal milk production and the protein nitrogen , but not the nonprotein nitrogen , fraction of human milk were relatively well-preserved in the presence of a short-term , marginal reduction of dietary protein The optimal quantity and quality of protein for low-birth-weight infants is undefined . In this study , 106 well , appropriate-for-gestational-age , low-birth-weight infants weighing 2,100 gm or less were divided into three gestational age groups and assigned r and omly within each age group to one of five feeding regimens : pooled human milk ; formula 1 ( protein content , 1.5 gm/100 ml- 60 parts bovine whey proteins to 40 parts bovine caseins ) ; formula 2 ( 3.0 gm/100 ml , 60:40 ) ; formula 3 ( 1.5 gm/100 ml , 18:82 ) ; and formula 4 ( 3.0 gm/100 ml , 18:82 ) . The concentrations of the free amino aicds in the plasma and urine of these infants were determined . The plasma concentrations of free amino acids were generally far greater in the infants fed the 3.0-gm/100 ml protein diets than they were in the infants fed pooled human milk . The plasma concentrations of free amino acids of the infants fed the 1.5-gm/100 ml protein diets were intermediate . In general , the concentrations of the free amino acids in the plasma of the infants fed the 3.0-gm/100 ml casein-predominant formula ( F4 ) were furthest from those fed pooled human milk . Glutamate showed the highest plasma amino acid concentrations in infants fed the 3.0-gm/100 ml casein-predominant formula ( F4 ) were furthest from those fed pooled human milk . Glutamate showed the highest plasma amino acid concentrations in infants fed both the high- and low-protein casein-predominant formulas . This was true despite the fact that the intake of glutamate on the high-protein , whey-predominant formula was twice that on the low-protein , casein-predominant formula . The differences between groups in the essential amino acids in plasma were generally greater than those of the nonessential amino acids . The concentrations of amino acids in the urine tended to parallel those of the plasma
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