Compared with casein or total milk protein, digestion of milk soluble proteins is too rapid to sustain the anabolic postprandial amino acid requirement.
BACKGROUND
The in vivo quality of milk protein fractions has seldom been studied in humans.


OBJECTIVE
Our objective was to compare the postprandial utilization of dietary nitrogen from 3 [(15)N]-labeled milk products: micellar caseins (MC), milk soluble protein isolate (MSPI), and total milk protein (TMP).


METHODS
The macronutrient intakes of 23 healthy volunteers were standardized for 1 wk, after which time the subjects ingested a meal containing MC (n = 8), MSPI (n = 7), or TMP (n = 8). [(15)N] was measured for an 8-h period in plasma amino acids, proteins, and urea and in urinary urea.


RESULTS
The transfer of dietary nitrogen to urea occurred earlier after MSPI ingestion than after MC and TMP ingestion, and concentrations remained high for 8 h, concomitantly with higher but transient hyperaminoacidemia and a higher incorporation of dietary nitrogen into plasma amino acids. In contrast, deamination, postprandial hyperaminoacidemia, and the incorporation of dietary nitrogen into plasma amino acids were lower in the MC and TMP groups. Finally, total postprandial deamination values were 18.5 +/- 2.9%, 21.1 +/- 2.8%, and 28.2 +/- 2.9% of ingested nitrogen in the TMP, MC, and MSPI groups, respectively.


CONCLUSIONS
Our results confirm the major role of kinetics in dietary nitrogen postprandial utilization and highlight the paradox of MSPI, which, despite its high Protein Digestibility Corrected Amino Acid Score, ensures a rate of amino acid delivery that is too rapid to sustain the anabolic requirement during the postprandial period. Milk proteins had the best nutritional quality, which suggested a synergistic effect between soluble proteins and caseins.
Lacroix
Magali
M
UMR INRA 914, Physiology of Nutrition and Feeding Control Unit, Institut National Agronomique Paris-Grignon, Paris, France.
Bos
Cécile
C
Léonil
Joëlle
J
Airinei
Gheorge
G
Luengo
Catherine
C
Daré
Sophie
S
Benamouzig
Robert
R
Fouillet
Hélène
H
Fauquant
Jacques
J
Tomé
Daniel
D
Gaudichon
Claire
C
D000328:Adult; D000596:Amino Acids / Q000097:blood / Q000378:metabolism* / Q000652:urine; D000818:Animals; D019540:Area Under Curve; D001806:Blood Urea Nitrogen; D001944:Breath Tests; D002153:Calorimetry, Indirect; D002245:Carbon Dioxide / Q000032:analysis; D002364:Caseins / Q000378:metabolism* / Q000493:pharmacokinetics; D004063:Digestion; D005260:Female; D006801:Humans; D007700:Kinetics; D008297:Male; D008892:Milk / Q000378:metabolism*; D008894:Milk Proteins / Q000378:metabolism* / Q000493:pharmacokinetics; D009587:Nitrogen Isotopes; D009753:Nutritive Value; D019518:Postprandial Period; D012995:Solubility; D014508:Urea / Q000652:urine
D000596:Amino Acids; D002364:Caseins; D008894:Milk Proteins; D009587:Nitrogen Isotopes; D002245:Carbon Dioxide; D014508:Urea