Elsevier

The Journal of Nutrition

Volume 153, Issue 4, April 2023, Pages 1063-1074
The Journal of Nutrition

Nutrient Requirements and Optimal Nutrition
Ileal Digestibility of Nitrogen and Amino Acids in Human Milk and an Infant Formula as Determined in Neonatal Minipiglets

https://doi.org/10.1016/j.tjnut.2023.02.025Get rights and content
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Abstract

Background

Infant formula (IF) has to provide at least the same amount of amino acids (AAs) as human milk (HM). AA digestibility in HM and IF was not studied extensively, with no data available for tryptophan digestibility.

Objectives

The present study aimed to measure the true ileal digestibility (TID) of total nitrogen and AAs in HM and IF to estimate AA bioavailability using Yucatan mini-piglets as an infant model.

Methods

Twenty-four 19-day-old piglets (males and females) received either HM or IF for 6 days or a protein-free diet for 3 days, with cobalt-EDTA as an indigestible marker. Diets were fed hourly over 6 h before euthanasia and digesta collection. Total N, AA, and marker contents in diets and digesta were measured to determine the TID. Unidimensional statistical analyses were conducted.

Results

Dietary N content was not different between HM and IF, while true protein was lower in HM (−4 g/L) due to a 7-fold higher non-protein N content in HM. The TID of total N was lower (P < 0.001) for HM (91.3 ± 1.24%) than for IF (98.0 ± 0.810%), while the TID of amino acid nitrogen (AAN) was not different (average of 97.4 ± 0.655%, P = 0.272). HM and IF had similar (P > 0.05) TID for most of the AAs including tryptophan (96.7 ± 0.950%, P = 0.079), except for some AAs (lysine, phenylalanine, threonine, valine, alanine, proline, and serine), with small significant difference (P < 0.05). The first limiting AA was the aromatic AAs, and the digestible indispensable AA score (DIAAS) was higher for HM (DIAASHM = 101) than for IF (DIAASIF = 83).

Conclusion

HM, compared to IF, had a lower TID for total N only, whereas the TID of AAN and most AAs, including Trp, was high and similar. A larger proportion of non-protein N is transferred to the microbiota with HM, which is of physiological relevance, although this fraction is poorly considered for IF manufacturing.

Keywords

human milk
infant nutrition
bioavailability
multiple hydrolysis
true digestibility
digestible indispensable AA score
tryptophan

Abbreviations

AA
Amino acid
DIAAS
Digestible indispensable amino acid score
HM
Human milk
HMO
Human milk oligosaccharide
IF
Infant formula
NPN
Non-protein nitrogen
PF
Protein-free
TID
True ileal digestibility

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