Effect of two amino acid solutions on leucine turnover in preterm infants

OBJECTIVE: To assess the effect of two different parenteral amino acid mixtures, Trophamine and Primene, on leucine turnover in preterm infants. METHOD: Leucine kinetics were measured with [5,5,5 D3]leucine tracer in 15 infants receiving Trophamine (group 'T') (mean birth weight 1,263 g) and 22 who received Primene (group 'P') (mean birth weight 1,336 g) during two study periods, within a few hours after birth but before introduction of parenteral amino acid solution, and again at postnatal day 7. The rate of appearance of leucine was calculated from the enrichment of alpha-ketoisocaproic acid in plasma. RESULTS: There were no significant differences in leucine turnover within a few hours after birth in the two groups. In the infants who received Primene leucine turnover on day 7 was significantly lower than in those who received Trophamine (269 +/- 43 vs. 335 +/- 27, p < 0.05). Despite a higher intake of leucine in the Trophamine group (108 +/- 10 vs. 77 +/- 8 micromol.kg(-1).h(-1)), leucine released from proteins at day 7 was higher in this group compared to Primene (227 +/- 27 vs. 192 +/- 42 micromol.kg(-1).h(-1)). CONCLUSIONS: Primene administration results in lower leucine released from proteins, an estimate of protein breakdown, than Trophamine in preterm infants. Increases in whole body leucine turnover in response to administration of i.v. amino acids is influenced by the composition of the amino acid mixture. The factors responsible for this difference remain to be elucidated.     

Effect of preeclampsia in the mother on the leucine metabolism in the newborn infant.

The leucine turnover in newborn infants is influenced by factors such as nutritional state and corticosteroid treatment. Little is known about maternal factors influencing the leucine turnover in the newborn. In order to approach the effect of preeclampsia in the mother on neonatal protein turnover, we studied the leucine turnover in preterm infants soon after birth and again after 7 days. Ten infants from preeclamptic mothers (birth weight 1,280 +/- 240 g, gestational age 31 +/- 2 weeks) and 15 control patients (birth weight 1,320 +/- 210 g, gestational age 30 +/- 2 weeks) were enrolled. The leucine turnover was measured using a primed constant 5-hour intravenous infusion of [1-(13)C]leucine within the first 24 h after delivery and again on day 7 of life. The turnover (leucine flux; micromol.kg(-1).h(-1)) was calculated from the enrichment in alpha-ketoisocaproic acid in plasma. The leucine turnover on day 1 was 300 +/- 65 in the preeclampsia group and 358 +/- 70 in the controls (ANOVA, p < 0.05). The values on day 7 were 474 +/- 73 in the preeclampsia group and 485 +/- 80 in the control group (n.s.). To conclude, the leucine turnover on day 1 is lower in infants of preeclamptic mothers as compared with controls. This difference has disappeared on day 7 of life after receiving the same protein and energy intake.     

Leucine kinetics during feeding in normal newborns

To examine how leucine and protein metabolism is affected by feeding, leucine kinetics were determined in 11 normal term newborns during feeding using a prime constant tracer infusion of 1-13C leucine combined with respiratory calorimetry. Fed newborns were compared with previously studied fasting newborns. Feeding and fasting newborns had similar rates of leucine oxidation (34 +/- 3 mumol/kg/h versus 31 +/- 4 mumol/kg/h) and leucine release from existing protein (156 +/- 16 mumol/kg/h versus 164 +/- 8 mumol/kg/h). In contrast, nonoxidative disposal rates of leucine (a reflection of protein synthesis) were significantly greater in feeding newborns (170 +/- 13 mumol/kg/h versus 129 +/- 9 mumol/kg/h). A significant positive correlation between birth weight and leucine flux was demonstrated in both feeding and fasting newborns. These results suggest that 1) newborns may accomplish protein accretion primarily by increases in protein synthesis rather than suppression of protein breakdown; 2) an estimate can be made of the minimal leucine intake required to replace irreversible leucine oxidative losses (816 mumol/kg/d, 107 mg/kg/d); and 3) the positive correlation between birth weight and leucine flux in both feeding and fasting newborns may be a result of differences in previous protein and energy supplies.     

Energy expenditure in human milk- versus formula-fed preterm infants

OBJECTIVE: We compared energy expenditure (EE) of preterm infants fed their mother's milk versus preterm infant formula.Study design A prospective, randomized crossover study of 13 healthy, appropriate weight for gestational age, gavage-fed, preterm infants. Before the study and according to our feeding protocol, infants uniformly received alternate feeds of human milk and formula. Each infant was randomly assigned to 24 hours of formula feeding followed by 24 hours of breast milk or the reverse. Infants were studied asleep, at the end of each 24-hour period. EE was measured by indirect calorimetry 1 hour before feeding, 20 minutes during feeding, and 1 hour after feeding in a servo-controlled convective incubator. Energy content of human milk was analyzed by bomb calorimetry. RESULTS: EE was significantly lower in breast milk-fed infants during prefeeding (52+/-6 vs 57+/-10 kcal/kg per 24 hours) (P<.05), per feeding (55+/-6 vs 60+/-10 kcal/kg per 24 hours) (P<.05), and at the postfeeding measurement (60+/-7 vs 65+/-7 kcal/kg per 24 hours) (P=.059). After correction of the results for the actual measured energy intake, all statistical differences reached the <.05 level. CONCLUSIONS: Preterm infants have lower EE when they are fed breast milk than when they are fed preterm infant formula.     

Leucine kinetics during simultaneously administered insulin and dexamethasone in preterm infants with severe lung disease

The objective of this study was to determine whether insulin administration would prevent the well-documented catabolic effect of dexamethasone given to preterm infants with chronic lung disease. We studied leucine metabolism in 11 very-low-birth-weight infants before dexamethasone treatment and on d 2, 4, and 7 thereafter. During the first 4 d of dexamethasone, insulin was administered i.v. at a dose of 0.5 (n = 7) or 1.0 (n = 5) IU/kg/d. Leucine turnover was not significantly different between d 0 (337 +/- 41.3 micromol leucine/kg/h), d 2 (288 +/- 27.2 micromol leucine/kg/h), d 4 (302 +/- 22.1 micromol leucine/kg/h), and d 7 (321 +/- 21.2 micromol leucine/kg/h), and neither was leucine breakdown (272 +/- 21.9 micromol leucine/kg/h on d 0, 225 +/- 21.5 micromol leucine/kg/h on d 2, 231 +/- 21 micromol leucine/kg/h on d 4, and 242 +/- 17.6 micromol leucine/kg/h on d 7). Weight gain rates were significantly lower during the first week of dexamethasone treatment compared with the week before treatment or the second and third week. We conclude that during insulin and corticosteroid administration in very-low-birth-weight infants, no changes were observed in leucine kinetics in contrast to previous studies. The decrease in weight gain was not reversed.     

Effect of low versus high intravenous amino acid intake on very low birth weight infants in the early neonatal period

Greater protein intakes are required than have been commonly used to achieve fetal in utero protein accretion rates in preterm neonates. To study the efficacy and safety of more aggressive amino acid intake, we performed a prospective randomized study in 28 infants [mean wt, 946 +/- 40 g (SEM)] of 1 (low amino acid intake, LAA) versus 3 g.kg(-1).d(-1) (high amino acid intake, HAA) at 52.0 +/- 3.0 h of life. After a minimum of 12 h of parenteral nutrition, efficacy was determined by protein balance and was significantly lower in the LAA versus HAA groups by both nitrogen balance (-0.26 +/- 0.11 versus 1.16 +/- 0.15 g.kg(-1).d(-1), p < 0.00005) and leucine stable isotope (0.184 +/- 0.17 versus 1.63 +/- 0.20 g.kg(-1).d(-1), p < 0.0005) methods. Leucine flux and oxidation and nonoxidative leucine disposal rates were all significantly higher in the HAA versus LAA groups (249 +/- 13 versus 164 +/- 8, 69 +/- 5 versus 32 +/- 3, and 180 +/- 10 versus 132 +/- 8 micro mol.kg(-1).h(-1), respectively, p < 0.005), but leucine appearance from protein breakdown was not (140 +/- 15 in HAA versus 128 +/- 8 micro mol.kg(-1).h(-1)). In terms of possible toxicity with HAA, there were no significant differences between groups in the amount of sodium bicarbonate administered, degree of acidosis as determined by base deficit, or blood urea nitrogen concentration. Parenteral HAA versus LAA intake resulted in increased protein accretion, primarily by increasing protein synthesis versus suppressing protein breakdown, and appeared to be well tolerated by very preterm infants in the first days of life.     

Whole body protein turnover and urea production of preterm small for gestational age infants fed fortified human milk or preterm formula

OBJECTIVES: To investigate protein metabolism and urea production in preterm small for gestational age neonates fed a preterm formula or fortified human milk. METHODS: Ten preterm small for gestational age neonates were fed either their own mother's milk fortified with a powdered protein mineral supplement or a special preterm formula. Protein metabolism was determined using constant steady-state infusion of L-[ring-2H5]phenylalanine and L-[1-13C]valine. Urea production was determined from steady-state [13C]urea kinetics. RESULTS: Mean protein intake was 24% higher in the preterm formula group than in the fortified human milk group. No differences in protein turnover, synthesis and breakdown were observed between the two groups, but protein accretion was 71% to 79% higher in the preterm formula group than the fortified human milk group. Urea production rates were not different in the two groups. There was a strong negative correlation between urea production and protein accretion calculated from phenylalanine kinetics but not when calculated from valine kinetics. CONCLUSIONS: Preterm formula and fortified human milk appear equally well tolerated by preterm small for gestational age neonates, but protein accretion was higher in the preterm formula group. In preterm small for gestational age infants, both phenylalanine and valine kinetic methods can be used to accurately determine protein metabolism.     

Energy expenditure and energy intake during dexamethasone therapy for chronic lung disease.

Dexamethasone is commonly administered to ventilator-dependent preterm infants with chronic lung disease. Infants receiving dexamethasone therapy frequently exhibit decreased rates of weight gain. The purpose of this investigation was to determine whether decreased growth in infants receiving dexamethasone therapy is caused by increased energy expenditure. Twelve infants were studied: 6 received dexamethasone treatment at 2 wk of age and crossed over to receive placebo treatment at 4 wk; the treatment order was reversed in the other 6 infants. The doubly labeled water method was used to determine energy expenditure for a 1-wk period during each treatment phase. The rate of weight gain during dexamethasone treatment was 6.5+/-10.6 and 20.0+/-5.7 g/kg/d during placebo treatment. Energy expenditure was 93.1+/-34.6 kcal/kg/d during dexamethasone treatment and 88.3+/-37.1 kcal/kg/d during placebo treatment. Energy intake was 119.2+/-29.0 kcal/kg/d during dexamethasone treatment and 113.8+/-23.7 kcal/kg/d during placebo treatment. The difference between intake and expenditure, or the energy available for growth, was 26.2+/-36.8 kcal/kg/d during dexamethasone treatment and 25.5+/-37.4 kcal/kg/d during placebo treatment. No significant differences were found in energy expenditure or energy intake between the treatment phases. The reduced growth seen in infants receiving dexamethasone treatment cannot be explained by increased energy expenditure or decreased energy intake, but may be due to differences in the composition of newly accreted tissue.     

Changes in protein turnover after the introduction of parenteral nutrition in premature infants: comparison of breast milk and egg protein-based amino acid solutions.

Rates of protein turnover were measured in 20 infants receiving either Vamin Infant (group A) or Vamin 9 glucose (group B) as the amino acid source in total parenteral nutrition. A constant infusion of L-[1-13C]leucine was used to measure whole body leucine flux, and leucine oxidation rates were derived from measurements of total urinary nitrogen excretion. Infants were first studied when receiving only i.v. glucose and again on each of the next 4 d as total parenteral nutrition was gradually increased to a maximum of 430 mg nitrogen/kg/d and 90 nonprotein kcal/kg/d. Net protein gain and protein synthesis and breakdown rates increased progressively for all infants taken together over the study period as i.v. nutrition was increasing (p less than 0.001). There were no differences between groups in the changes in net protein gain and rates of protein synthesis and breakdown throughout the study period. Nitrogen retention on d 5 for the two groups was similar (60 +/- 16% and 67 +/- 11% in groups A and B, respectively). In a subgroup of infants, measurements were repeated on d 8, when the intake had been constant for 3 d. Protein retention was the same as on d 5, but both synthesis and breakdown were increased. It is concluded that rates of protein turnover increase significantly in response to increasing i.v. nutrition and that this elevation was not influenced by the composition of the amino acid mixture given.     

Glutamine supplement with parenteral nutrition decreases whole body proteolysis in low birth weight infants

OBJECTIVES: To examine the effect of supplemental glutamine (0.6 g.kg -1 .d -1 ) on whole body protein/nitrogen and glutamine kinetics in low birth weight (LBW) infants receiving parenteral nutrition in the immediate neonatal period. STUDY DESIGN: Premature infants < or =32 weeks gestation with a birth weight from 694 to 1590 g were randomly assigned to either a glutamine-supplemented group (n = 10) or to a control group (n = 10). Tracer isotope studies were performed when the infants were 6 to 7 days old and had been receiving an amino acid intake of approximately 3.0 g.kg -1 .d -1 for at least 3 days. Whole body glutamine and nitrogen kinetics were measured with [5-15N]glutamine, [2H5]phenylalanine, [1-13C, 15 N]leucine, [15N2]urea, and GC-mass spectrometry. RESULTS: Supplemental glutamine was associated with a lower rate of appearance of glutamine ( P = .003), phenylalanine ( P = .001), and leucine C ( P = .003). There was no significant difference in leucine N turnover, urea turnover and plasma cortisol, and C-reactive protein levels in the 2 groups. CONCLUSION: Parenteral glutamine supplement in LBW infants was associated with lower whole-body protein breakdown. Because the decrease in whole body proteolysis is associated with protein accretion, parenteral glutamine supplement may be beneficial in selected populations of LBW infants.     

Minimum protein intake for the preterm neonate determined by protein and amino acid kinetics

Lower limits of protein needs in prematurely born neonates have not been adequately studied, yet providing protein in amounts maximizing accretion without excess is a goal in these infants' nutritional care. We hypothesized that with the use of amino acid oxidation methodology, it would be possible to define minimum protein requirement. Our objective was to investigate protein kinetics during short-term changes in protein intake by measurement of nitrogen balance and amino acid flux and oxidation using [(15)N]glycine, [(13)C]phenylalanine, and [(13)C]leucine tracers. Protein kinetics were examined in 21 preterm infants (gestational age: 29 +/- 3 wk; birth weight: 1091 +/- 324 g) at five protein intakes (1.0, 1.5, 2.0, 2.5, and 3.0 g x kg(-1) x d(-1)) with 1 d of adaptation to the test intakes. From nitrogen balance data, a protein need of 0.74 g x kg(-1 x -1) was estimated to achieve zero balance. For all three amino acids, flux and oxidation estimates were not different across protein intakes. Whole-body protein synthesis and breakdown estimates from [(15)N]ammonia data were 14.6 +/- 3.4 and 14.4 +/- 4.1 g x kg(-1) x d(-1), respectively. Glycine flux (680 +/- 168 micromol x kg(-1) x h(-1)) was greater than leucine flux (323 +/- 115 micromol x kg(-1) x h(-1)), which was greater than phenylalanine flux (84.3 +/- 35.2 micromol x kg(-1) x h(-1)). Leucine oxidation (36.7 +/- 15.6 micromol x kg(-1) x h(-1)) was also greater than phenylalanine oxidation (6.64 +/- 4.41 micromol x kg(-1) x h(-1)). Infants in our study were able to adapt to short-term changes in protein intake with little consequence to the overall whole-body protein economy, as measured by the three test amino acids.     

Effect of minimal enteral feeding on splanchnic uptake of leucine in the postabsorptive state in preterm infants

We conducted a controlled, randomized trial to study the effect of minimal enteral feeding on leucine uptake by splanchnic tissues, as an indicator of maturation of these tissues, in preterm infants in the first week of life. Within a few hours after birth, while receiving only glucose, a primed constant infusion of [1-(13)C]-leucine was started and continued for 5 h via the nasogastric tube, whereas 5,5,5 D3-leucine was infused intravenously (for both tracers, priming dose 2 mg/kg, continuous infusion 2 mg/kg/h). Patients were thereafter randomized to receive solely parenteral nutrition (C), parenteral nutrition and 20 mL breast milk/kg/d (BM), or parenteral nutrition and 20 mL formula/kg/d (F). On d 7, the measurements were repeated, after discontinuing the oral intake for 5 h. Fourteen infants were included in group C, 12 in group BM, and 12 in group F. There was no difference in energy intake or nitrogen balance at any time. On d 1, plasma enrichment for the nasogastric tracer was lower than for the intravenous tracer for all three groups, both for leucine and for alpha-keto-isocaproic acid. On d 7, the enrichment for leucine and alpha-keto-isocaproic acid for the nasogastric tracer was lower than for the intravenous tracer for the groups BM and F (BM: 3.65 +/- 1.20 nasogastric versus 4.64 +/- 0.64 i.v.; F: 4.37 +/- 1.14 nasogastric versus 5.21 +/- 0.9 i.v.). In the control group, there was no difference between tracers. The lower plasma enrichment for the nasogastric tracer compared with the intravenous tracer suggests uptake of leucine by the splanchnic tissues. We conclude that minimal enteral feeding--even in low volumes of 20 mL/kg/d--increases the leucine uptake by the splanchnic tissue. We speculate that this reflects a higher protein synthesis of splanchnic tissues in the groups receiving enteral nutrition.     

Partition of nitrogen intake and excretion in low-birth-weight infants

Although nitrogen balance studies have been carried out in low-birth-weight infants, few have partitioned the nitrogen into its components. In this study, 72-hour balance studies were conducted in 24 low-birth-weight infants (gestational age, 30.7 +/- 1.6 weeks; birth weight 1.36 +/- 0.25 kg) fed their mothers' milk (preterm milk) or 50% preterm milk and 50% formula. Total nitrogen, nonprotein nitrogen, and whey protein intake and excretion were measured. Total nitrogen intake (preterm milk group, 452 +/- 138 mg/kg per day; preterm + formula group, 406 +/- 93 mg/kg per day), absorption (85%), and retention (71%) were not significantly different between groups. Intact and fragments of secretory IgA and lactoferrin were detected in soluble fecal extracts, and represented 25% and 9% of intake, respectively. Feeding preterm milk allows for nitrogen accretion similar to intrauterine growth rates for 5 weeks postnatally, and provides potentially functional proteins for the low-birth-weight infant.     

Acute effects of intravenous glutamine supplementation on protein metabolism in very low birth weight infants: a stable isotope study.

Although very low birth weight infants are subjected to severe stress and glutamine is now considered a conditionally essential amino acid that may attenuate stress-induced protein wasting in adults, current amino acid solutions designed for neonatal parenteral nutrition do not contain glutamine. To determine whether a short-term supplementation with i.v. glutamine would affect protein metabolism in very low birth weight infants, 13 preterm neonates (gestational age, 28-30 wk; birth weight, 820-1610 g) receiving parenteral nutrition supplying 1.5 g x kg(-1) x d(-1) amino acids and approximately 60 nonprotein kcal x kg(-1) x d(-1) were randomized to receive an i.v. supplement made of either 1) natural L-glutamine (0.5 g x kg(-1) x d(-1); glutamine group), or 2) an isonitrogenous glutamine-free amino acid mixture (control group), for 24 h starting on the third day of life. On the fourth day of life, they received a 2-h infusion of NaH(13)CO(3) to assess the recovery of (13)C in breath, immediately followed by a 3-h L-[1-(13)C]leucine infusion. Plasma ammonia did not differ between the groups. Glutamine supplementation was associated with 1) higher plasma glutamine (629 +/- 94 versus 503 +/- 83 microM, mean +/- SD; p < 0.05, one-tailed unpaired t test), 2) lower rates of leucine release from protein breakdown (-16%, p < 0.05) and leucine oxidation (-35%, p < 0.05), 3) a lower rate of nonoxidative leucine disposal, an index of protein synthesis (-20%, p < 0.05), and 4) no change in protein balance (nonoxidative leucine disposal - leucine release from protein breakdown, NS). We conclude that although parenteral glutamine failed to enhance rates of protein synthesis, glutamine may have an acute protein-sparing effect, as it suppressed leucine oxidation and protein breakdown, in parenterally fed very low birth weight infants.     

Energy expenditure and deposition of breast-fed and formula-fed infants during early infancy

The energy intake, expenditure, and deposition of 40 breast-fed and formula-fed infants were investigated at 1 and 4 mo of age to explore possible differences in energy utilization between feeding groups. Energy intake was calculated from 5-d test-weighing records or pre- and postweighing of formula bottles, in combination with bomb calorimetry of the milks. Total daily energy expenditure (TDEE) was determined by the doubly labeled water method. Sleeping metabolic rate (SMR) and minimal observable energy expenditure were measured by indirect calorimetry. Activity was estimated as the difference between TDEE and SMR. Energy deposition was estimated from dietary intake and TDEE. Energy intakes were significantly higher for the formula-fed than breast-fed infants at 1 mo (118 +/- 17 versus 101 +/- 16 kcal/kg/d) and 4 mo (87 +/- 11 versus 72 +/- 9 kcal/kg/d) (p less than 0.001). TDEE averaged 67 +/- 8 and 64 +/- 7 kcal/kg/d at 1 mo and 73 +/- 9 and 64 +/- 8 kcal/kg/d at 4 mo for the formula-fed and breast-fed infants, respectively, and differed between feeding groups (p less than 0.04). SMR and minimal observable energy expenditure (kcal/min) were higher among the formula-fed infants at 1 and 4 mo (p less than 0.005). The energy available for activity and the thermic effect of feeding did not differ between feeding groups. Rates of weight gain (g/d) and energy deposition (kcal/kg/d) tended to be greater among the formula-fed infants at 1 and 4 mo (p less than 0.006).(ABSTRACT TRUNCATED AT 250 WORDS)     

Nutrient balance, energy utilization, and composition of weight gain in very-low-birth-weight infants fed pooled human milk or a preterm formula

Growth, protein, and energy balances were studied in two groups of very-low-birth-weight premature infants fed pooled pasteurized human milk (HM) or a preterm formula (PF). Each infant was studied at 33 and 36 weeks gestational age with a combined technique of nutrient balance and indirect calorimetry measurement. Weight and length gains were higher with PF than with HM, but head circumference growth was similar with both milks. Although the volume of milk given was lower, energy intake was higher with PF than with HM in both studies (126 to 130 vs 103 to 109 kcal/kg/day). Percentage of energy absorbed was better with PF than with HM (94% vs 84%) at 33 weeks, and similar (95%) with both milks at 36 weeks. Energy expenditure, which had increased from 33 weeks to 36 weeks, was higher with PF than with HM (57 to 63 vs 46 to 52 kcal/kg/day) during both studies. Energy retention accounted for about 50% of energy absorbed with both milks, but was higher with PF than with HM (60 vs 40 to 50 kcal/kg/day) in both studies, and resulted in fat accretion well above that seen during intrauterine growth for both milks in both studies. Protein intake was higher with PF than with HM (3.1 vs 2.4 gm/kg/day) in both studies, giving a protein accretion similar to the intrauterine accretion with PF (2.2 gm/kg/day), but lower with HM. Our results suggest that the nutritional value of pooled pasteurized human milk for VLBW infants should be reconsidered, especially because of its low protein content, and that energy density of preterm formulas must be questioned in view of elevated fat deposition.     

Whole body protein synthesis and energy expenditure in very low birth weight infants

The aim of the present work was to study whole body protein synthesis and breakdown, as well as energy metabolism, in very low birth weight premature infants (less than 1500 g) during their rapid growth phase. Ten very low birth weight infants were studied during their first and second months of life. They received a mean energy intake of 114 kcal/kg X day and 3 g protein/kg X day as breast milk or milk formula. The average weight gain was 15 g/kg X day. The apparent energy digestibility was 88%, i.e. 99 kcal/kg X day. Their resting postprandial energy expenditure was 58 kcal/kg X day, indicating that 41 kcal/kg X day was retained. The apparent protein digestibility was 89%, i.e. 2.65 g/kg X day. Their rate of protein oxidation was 0.88 g/kg X day so that protein retention was 1.76 g/kg X day. There was a linear relationship between N retention and N intake (r = 0.78, p less than 0.001). The slope of the regression line indicates a net efficiency of N utilization of 67%. Estimates of body composition from the energy balance, coupled with N balance method, showed that 25% of the gain was fat and 75% was lean tissue. Whole body protein synthesis and breakdown were determined using repeated oral administration of 15N glycine for 60-72 h, and 15N enrichment in urinary urea was measured. Protein synthesis averaged 11.2 g/kg X day and protein breakdown 9.4 g/kg X day. Muscular protein breakdown, as estimated by 3-methylhistidine excretion, contributed to 12% of the total protein breakdown.(ABSTRACT TRUNCATED AT 250 WORDS)     

Growth of very low birth weight infants on varying amounts of human milk protein

In a double-blind, randomized study, 28 healthy, growing very low birth wt, appropriate-for-gestational-age infants were fed human milk, preferably mother's own, fortified daily with human milk protein and/or human milk fat. The infants entered the study when they were stable on complete enteral intakes of 170 mL/kg/d (mean age = 19 d). The study lasted for a mean of 4 wk. Samples from all the milks were collected daily, and intakes of protein, fat, carbohydrates, energy, and electrolytes were calculated weekly during the whole study period. Protein intakes ranged from 1.7 to 3.9 g/kg/d, and energy intakes from 100 to 150 kcal/kg/d. Wt and length gain in the nonprotein-enriched groups were 15.6 +/- 2.7 g/kg/d (mean +/- SD) and 0.88 +/- 0.17 cm/wk; the corresponding figures for the protein-enriched groups were 20.2 +/- 2.1 g/kg/d and 1.24 +/- 0.14 cm/wk. There was a strong correlation between protein intake and growth in wt and length up to an intake of about 3 g/kg/d; more protein did not result in increased growth. The same was true for energy intake, with a maximal growth rate at an intake of about 120 kcal/kg/d. A protein intake of more than 3 g/kg/d resulted in a growth rate equal to or higher than the estimated intrauterine growth rate. Some infants fed mature banked human milk alone had a poor growth. Sodium intake was low, ranging from 1.5 to 2.6 mmol/kg/d. No correlation was found between sodium intake and growth rates.     

15N-tracer investigations into the nitrogen metabolism of preterm infants fed mother's milk and a formula diet

Protein synthesis, protein breakdown, protein-N turnover, and other parameters describing the nitrogen metabolism were measured in five male preterm infants. The weight of the subjects at birth was 2,064 +/- 107 g and the measurements were performed at age 16.0 +/- 4.5 days in the case of the mother's milk diet and 27.4 +/- 6.8 days in the case of the formula diet containing 1.8% protein. The parameters were measured by means of the 15N-tracer technique using [15N]glycine (95 atom %) applied in a single oral dose of 20 mg/kg as a tracer. The three-pool model proposed by Winkler and Faust was used to calculate the whole body protein parameters. No difference in net protein gain, protein synthesis, protein breakdown, or the other protein metabolism parameters were recorded despite the different protein inputs. Renal nitrogen excretion and the rate of endogenous urea N excretion were significantly higher for the formula diet than for the mother's milk diet. The protein synthesis rate of 7.9 g X kg-1 X day-1 was, as has previously been observed, higher than in other age groups. The protein metabolism of the preterm infant older than 33 weeks of gestational age does not benefit from a formula diet based on cow's milk that is richer in protein than mother's milk.     

Postdischarge formula consumption in infants born preterm.

In 31 infants born preterm and formula fed ad libitum, all milk intake was weighed from hospital discharge to nine months post-term. Mean daily milk intake was high, reaching 230 g/kg before four weeks post-term and was still over 150 g/kg beyond six months. Five of the 31 infants (16%) consumed 300-350 g/kg; 50% 'voluntarily' consumed more than upper recommended limits for energy intake and 35% did so for protein intake.