[show abstract][hide abstract] ABSTRACT: Background:We determined the effect of adaptation to the study diet on the oxidation of the indicator amino acid and the required tracer washout time in preterms.Methods:Subjects received a study diet for 6d that entailed a 50% reduction in leucine. Tracer studies using enterally infused [(13)C]bicarbonate and [1-(13)C]phenylalanine were performed on days 1, 2, 4 and 6. Breath samples containing (13)CO(2) were collected during steady state, measured by infrared spectrometric analysis and the fraction of (13)CO(2) recovery from (13)C oxidation (F(13)CO(2)) was calculated.Results:Preterm infants (n=11, birth weight 1.9 ± 0.1 kg, gestational age 32.6 ± 1.5 wks) received 166 mg∙kg(-1)∙d(-1) of leucine. Baseline enrichment changed significantly at day 1 of the study diet. F(13)CO(2) did not change significantly between days 2 and 4 but was significantly lower at day 6. The tracer washout time was determined 7.5 h using a biphasic regression analysis.Conclusion:One day of adaptation to a new diet is necessary to adapt to the (13)C enrichment of the study formula before starting infant requirement studies. Adaptation for a period of 5 d results in a protein sparing response. The minimal time between two studies within the same subject is 7.5 h.Pediatric Research (2013); doi:10.1038/pr.2013.31.
[show abstract][hide abstract] ABSTRACT: Infant nutrition has a major impact on child growth and functional development. Low and high intakes of protein or amino acids could have a detrimental effect.
The objective of the study was to determine the lysine requirement of enterally fed term neonates by using the indicator amino acid oxidation (IAAO) method. L-[1-(13)C]phenylalanine was used as an indicator amino acid.
Twenty-one neonates were randomly assigned to lysine intakes that ranged from 15 to 240 mg · kg(-1) · d(-1). Breath, urine, and blood samples were collected at baseline and during the plateau. The mean lysine requirement was determined by using biphasic linear regression crossover analysis on the fraction of (13)CO(2) recovery from L-[1-(13)C]phenylalanine oxidation (F(13)CO(2)) and phenylalanine oxidation rates calculated from the L-[1-(13)C]phenylalanine enrichment of urine and plasma.
The mean (±SD) phenylalanine flux calculated from urine and plasma L-[1-(13)C]phenylalanine enrichment data were 88.3 ± 6.9 and 84.5 ± 7.4 μmol · kg(-1) · h(-1), respectively. Graded intakes of lysine had no effect on phenylalanine fluxes. The mean lysine requirement determined by F(13)CO(2) was 130 mg · kg(-1) · d(-1) (upper and lower CIs: 183.7 and 76.3 mg · kg(-1) · d(-1), respectively). The mean requirement was identical to the requirement determined by using phenylalanine oxidation rates in urine and plasma.
The mean lysine requirement of enterally fed term neonates was determined by using F(13)CO(2) and phenylalanine oxidation rates calculated from the L-[1-(13)C]phenylalanine enrichment of urine and plasma. These methods yielded a similar result of 130 mg lysine · kg(-1) · d(-1). This study demonstrates that sampling of (13)CO(2) in expired air is sufficient to estimate the lysine requirement by using the IAAO method in infants. This trial was registered at www.trialregister.nl as NTR1610.
American Journal of Clinical Nutrition 11/2011; 94(6):1496-503. · 6.50 Impact Factor
[show abstract][hide abstract] ABSTRACT: The intestine is a major site of amino acid metabolism, especially in neonates. Neonatal animals derive energy needed for metabolic processes from dietary glucose and amino acids. Rats were found to oxidize non-essential amino acids such as aspartate, glutamate and glutamine in the intestine at a high rate. We have previously found that glutamate and glucose are important sources of energy for the splanchnic tissues in fully fed preterm infants. However, no data are available on splanchnic aspartate metabolism in human preterm infants. In the present study we studied whole-body and splanchnic aspartate metabolism and determined the metabolic fate of aspartate.
In eight, enterally fed, preterm infants (gestational age 31 weeks (wk)+/-3 SD, range: 26-34wk) splanchnic and whole-body aspartate kinetics were assessed by dual tracer ([U-(13)C]aspartate and [D(3)]aspartate) techniques.
Splanchnic first-pass aspartate uptake was almost complete (77+/-15%). Almost all (80+/-9%) of the (13)C administered as [U-(13)C]aspartate used in first-pass was recovered as CO(2) in expired breath.
The splanchnic tissues extract almost all of the dietary aspartate in preterm infants. The majority of the labeled carbon is recovered in expired breath, making it most likely that the sequestered carbon skeleton of aspartate is utilized for energy generation.