Plasma amino acids in term neonates after a feed of human milk or formula. II. Characteristic changes in individual amino acids

Metabolic phenotype of breast-fed infants, and infants fed standard formula or bovine MFGM supplemented formula: a randomized controlled trial

Formula-fed (FF) infants exhibit a different metabolic profile than breast-fed (BF) infants. Two potential mechanisms are the higher protein level in formula compared with breast milk and the removal of the milk fat and associated milk fat globule membranes (MFGM) during production of infant formula. To determine whether MFGM may impact metabolism, formula-fed infants were randomly assigned to receive either an MFGM isolate-supplemented experimental formula (EF) or a standard formula (SF) from 2 until 6 months and compared with a BF reference group. Infants consuming EF had higher levels of fatty acid oxidation products compared to infants consuming SF. Although the protein level in the study formula was approximately 12 g/L (lower than most commercial formulas), a metabolic difference between FF and BF remained such that FF infants had higher levels of amino acid catabolism by-products and a low efficiency of amino acid clearance (preference for protein metabolism). BF infants had higher levels of fatty acid oxidation products (preference for fat metabolism). These unique, energy substrate-driven metabolic outcomes did not persist after diet was shifted to weaning foods and appeared to be disrupted by complementary feeding. Our results suggest that MFGM may have a role in directing infant metabolism.

Effects of infant formula composition on long-term metabolic health

Early nutrition may have long-lasting metabolic impacts in adulthood. Even though breast milk is the gold standard, most infants are at least partly formula-fed. Despite obvious improvements, infant formulas remain perfectible to reduce the gap between breastfed and formula-fed infants. Improvements such as reducing the protein content, modulating the lipid matrix and adding prebiotics, probiotics and synbiotics, are discussed regarding metabolic health. Numerous questions remain to be answered on how impacting the infant formula composition may modulate the host metabolism and exert long-term benefits. Interactions between early nutrition (composition of human milk and infant formula) and the gut microbiota profile, as well as mechanisms connecting gut microbiota to metabolic health, are highlighted. Gut microbiota stands as a key actor in the nutritional programming but additional well-designed longitudinal human studies are needed.

Amino acid profiles in term and preterm human milk through lactation: a systematic review

Amino acid profile is a key aspect of human milk (HM) protein quality. We report a systematic review of total amino acid (TAA) and free amino acid (FAA) profiles, in term and preterm HM derived from 13 and 19 countries, respectively. Of the 83 studies that were critically reviewed, 26 studies with 3774 subjects were summarized for TAA profiles, while 22 studies with 4747 subjects were reviewed for FAA. Effects of gestational age, lactation stage, and geographical region were analyzed by Analysis of Variance. Data on total nitrogen (TN) and TAA composition revealed general inter-study consistency, whereas FAA concentrations varied among studies. TN and all TAA declined in the first two months of lactation and then remained relatively unchanged. In contrast, the FAA glutamic acid and glutamine increased, peaked around three to six months, and then declined. Some significant differences were observed for TAA and FAA, based on gestational age and region. Most regional TAA and FAA data were derived from Asia and Europe, while information from Africa was scant. This systematic review represents a useful evaluation of the amino acid composition of human milk, which is valuable for the assessment of protein quality of breast milk substitutes.

Early diet impacts infant rhesus gut microbiome, immunity, and metabolism

Epidemiological research has indicated a relationship between infant formula feeding and increased risk of chronic diseases later in life including obesity, type-2 diabetes, and cardiovascular disease. The present study used an infant rhesus monkey model to compare the comprehensive metabolic implications of formula- and breast-feeding practices using NMR spectroscopy to characterize metabolite fingerprints from urine and serum, in combination with anthropometric measurements, fecal microbial profiling, and cytokine measurements. Here we show that formula-fed infants are larger than their breast-fed counterparts and have a different gut microbiome that includes higher levels of bacteria from the Ruminococcus genus and lower levels of bacteria from the Lactobacillus genus. In addition, formula-fed infants have higher serum insulin coupled with higher amino acid levels, while amino acid degradation products were higher in breast-fed infants. Increases in serum and urine galactose and urine galactitol were observed in the second month of life in formula-fed infants, along with higher levels of TNFα, IFN-γ, IL-1β, IL-4, and other cytokines and growth factors at week 4. These results demonstrate that metabolic and gut microbiome development of formula-fed infants is different from breast-fed infants and that the choice of infant feeding may hold future health consequences.

Nutrient requirements for preterm infant formulas

Achieving appropriate growth and nutrient accretion of preterm and low birth weight (LBW) infants is often difficult during hospitalization because of metabolic and gastrointestinal immaturity and other complicating medical conditions. Advances in the care of preterm-LBW infants, including improved nutrition, have reduced mortality rates for these infants from 9.6 to 6.2% from 1983 to 1997. The Food and Drug Administration (FDA) has responsibility for ensuring the safety and nutritional quality of infant formulas based on current scientific knowledge. Consequently, under FDA contract, an ad hoc Expert Panel was convened by the Life Sciences Research Office of the American Society for Nutritional Sciences to make recommendations for the nutrient content of formulas for preterm-LBW infants based on current scientific knowledge and expert opinion. Recommendations were developed from different criteria than that used for recommendations for term infant formula. To ensure nutrient adequacy, the Panel considered intrauterine accretion rate, organ development, factorial estimates of requirements, nutrient interactions and supplemental feeding studies. Consideration was also given to long-term developmental outcome. Some recommendations were based on current use in domestic preterm formula. Included were recommendations for nutrients not required in formula for term infants such as lactose and arginine. Recommendations, examples, and sample calculations were based on a 1000 g preterm infant consuming 120 kcal/kg and 150 mL/d of an 810 kcal/L formula. A summary of recommendations for energy and 45 nutrient components of enteral formulas for preterm-LBW infants are presented. Recommendations for five nutrient:nutrient ratios are also presented. In addition, critical areas for future research on the nutritional requirements specific for preterm-LBW infants are identified.

"Hypotyrosinemia" in phenylketonuria

It has been postulated that the significant incidence of learning disabilities in well-treated patients with phenylketonuria (PKU) may be due, in part, to reduced production of neurotransmitters as a result of deficient tyrosine transport across the neuronal cell membrane. Hypotyrosinemia has been reported in treated and untreated PKU but virtually no data are available. We decided to examine this in our patient population and to compare it with the published norms, patient data from our hospital clinical biochemical laboratory database, and a group of normal children and adolescents in a private pediatric practice. We found that the mean nonfasting plasma tyrosine in 99 classical PKU patients was 41.1 micromol/L, in 26 mild (atypical) PKU patients 53.3 micromol/L, and in 35 non-PKU mild hyperphenylalaninemia patients 66.6 micromol/L. This compared to nonfasting plasma tyrosine levels in 102 non-PKU subjects of 64.0 micromol/L in our hospital biochemistry database, 69.1 micromol/L in 58 volunteers in the private office practice, and 64-78.8 micromol/L in infants, children, and adolescents in the literature review. Our data support the previously undocumented statements in the literature that plasma tyrosine levels are low in PKU.

Plasma amino acid concentrations, indexes of protein metabolism and growth in healthy, full-term infants fed partially hydrolyzed infant formula

BACKGROUND

It has been reported that feeding extensively hydrolyzed infant formula influenced the availability of arginine, glycine, histidine, lysine and threonine in full-term infants investigated during the first 2 months of life. In the present study, the nutritional effects of feeding partially hydrolyzed formula (PHF) were investigated.

METHODS

Term infants fed conventional formula (F; n = 11) or PHF (n = 11) were investigated at the ages of 5, 30, 60, 90, and 120 days. Anthropometric data were obtained, and plasma amino acid concentrations and biochemical indices of protein metabolism were measured.

RESULTS

Plasma concentrations (in micromoles per liter) of lysine on day 90: 117 (21) versus 143 (24); of threonine on day 30: 140 (53) versus 263 (87); of ornithine on day 90: 56 (21) versus 78 (29); and of tyrosine on day 30: 52 (17) versus 77 (20), on day 60: 56 (14) versus 87 (19) and on day 90: 46 (9) versus 81 (17) were significantly lower in infants receiving PHF than in those fed F. Values are median (range from 1st to 3rd quartile), PHF versus F; p < 0.05. At day 120, infants fed PHF showed significantly lower serum albumin concentrations than did infants receiving F (43.3 +/- 3.4 versus 48.9 +/- 3.5, g/l; mean +/- SD; p < 0.05). Serum creatinine, urea nitrogen, uric acid and total protein concentrations and gain in weight, length, and head circumference did not differ throughout the study.

CONCLUSIONS

In this study, feeding PHF did not affect the majority of plasma amino acid concentrations, some indices of protein metabolism, and basic parameters of growth in full-term infants. However, plasma concentrations of lysine, threonine, tyrosine, ornithine, and albumin were, on at least one occasion, significantly lower in infants fed PHF than in those receiving F.

Plasma amino acid concentrations in healthy, full-term infants fed hydrolysate infant formula

The effect of feeding hydrolysate infant formula (HF) on protein and amino acid metabolism was investigated in healthy, full-term infants who were either breast-fed (BF, n = 10) or received conventional formula (CF, n = 10) or HF based on soy and beef collagen (n = 10) with equal total protein equivalent contents. There were no differences between groups for gain in weight, length, and head and chest circumferences throughout the study. Plasma concentrations of total proteins, albumin, urea nitrogen, uric acid, and creatinine as well as total amino acid and total essential amino acid concentrations did not differ at the ages of 2, 4, and 8 weeks. In contrast, significant differences were seen in concentrations of five free amino acids. Arginine concentrations were significantly higher at the age of 4 weeks in the infants fed HF than in the other groups (71 +/- 12 versus 27 +/- 6 and 30 +/- 4, mumol/L, mean +/- SEM, HF versus BF and CF, p < 0.01). Plasma histidine concentrations were also higher in infants receiving HF (4 weeks: 217 +/- 33 versus 91 +/- 18, HF versus BF, p < 0.01; 8 weeks: 218 +/- 33 versus 105 +/- 20, HF versus CF, p < 0.01). The most pronounced feeding-related differences were seen in plasma glycine concentrations (2 weeks: 653 +/- 89 versus 345 +/- 55, HF versus BF, p < 0.01; 8 weeks: 613 +/- 74 versus 385 +/- 56 and 312 +/- 46, HF versus BF and CF, p < 0.01), with the mean value exceeding the upper limit of the normal range in infants fed HF. Although the biological importance of the differences observed remains to be clarified, further investigations on amino acid metabolism are needed to establish the final nutritional safety of feeding hydrolysate infant formulae.

Plasma amino acid patterns in very low birth weight infants during parenteral nutrition

Plasma amino acids were measured in eight very low birth weight infants (less than or equal to 1000 gm) before and after infusion of parenteral alimentations with Freamine III. Significant elevation in serum threonine, valine, isoleucine, methionine, serine, proline, glycine and ornithine was noted after twenty four hours of infusion. On the other hand, significant decreases in taurine and tyrosine levels were noted. Our study suggests that current solution is not optimal for premature neonates and the amount of protein administered during the first week in infants weighing less than or equal to 1000 gm should be decreased from the recommended 2.5-3.0 gm/kg/day.

Plasma amino acids in term neonates and infants with phenylketonuria before and after institution of the diet

The plasma amino acid concentrations were measured in 12 neonates with phenylketonuria (PKU). Blood samples were taken when fasting and two hours after a meal. The individual amino acid concentrations, the glycine/valine ratios, and the total amino acid concentrations were mutually compared and also compared to reference intervals. When the diet was instituted and plasma phenylalanine decreased, we observed a normalization of the postprandial response of isoleucine, leucine, tyrosine, and valine.

Plasma amino acids in preterm infants after a feed of human milk or formula

Prefeeding and sequential postprandial plasma amino acid concentrations were measured in 31 healthy preterm infants with gestational ages between 33 and 37 weeks at the ages of 4 to 12 days, to characterize changes after quantitatively and qualitatively different protein loads. All infants had previously been fed with human milk. The infants received a normal feed of pooled human milk (true protein 0.8 gm/dl) or of adapted or nonadapted milk formula (protein 1.5 gm/dl) from a bottle. The concentrations of all essential and several nonessential amino acids, including arginine and ornithine, rose sharply in plasma. Glycine decreased, and alanine increased slowly. Postprandial alterations in plasma total amino acids seemed to reflect the protein content of the different milks. In preterm infants, fed at three- to four-hour intervals, plasma amino acid concentrations fluctuate continuously. Thus in long-term studies and in screening, samples should be taken immediately before feeds. Postprandial plasma amino acid measurements may prove to be a useful means for testing the infant's ability to handle the protein or individual amino acid loads in various feeds.

Plasma amino acids in term neonates after a feed of human milk or formula. I. Total amino acids and glycine/valine ratios as reflectors of protein intake

Human milk and formulas with different quantities and qualities of protein were compared by measuring sequential postprandial changes in total amino acids and glycine/valine ratios in plasma of 23 healthy term neonates who had previously been breast-fed ad libitum. At the mean age of 5.5 days the infants received from a bottle 1/36 of their body weight of banked human milk (true protein 0.8 g/100 ml), or formula (1.5 g/100 ml of protein, whey-to-casein ratio 60 : 40 (adapted) or 18 : 82 (non-adapted), or 3.0 g/ml of protein, 60 : 40) after a 3.5-4 hour fast. After the feed, the sum of plasma free amino acids rose and the glycine/valine ratio fell, these changes being significant as soon as 30 min after the start of feeding and maximal at 30 min after human milk but at 60 min after the formulas. Both values returned to prefeeding levels, after human milk in 2-3 hours and after the two 1.5 g/100 ml formulas in about 4 hours, but after the 3 g/100 ml formula were still notably altered at 3.5 hours. The postprandial changes measured seemed to reflect dietary protein intake, and to be unaffected by protein quality (adapted vs. non-adapted formulas). The results show that in studies of plasma amino acids in young infants sampling times should be standardized exactly with respect to type of previous feeding and duration of fasting.