title: Compared with casein or total milk protein, digestion of milk soluble proteins is too rapid to sustain the anabolic postprandial amino acid requirement.
abstract: 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.
authors.affiliation: UMR INRA 914, Physiology of Nutrition and Feeding Control Unit, Institut National Agronomique Paris-Grignon, Paris, France.
authors.forename: Magali
authors.initials: M
authors.lastname: Lacroix
authors.forename: Cécile
authors.initials: C
authors.lastname: Bos
authors.forename: Joëlle
authors.initials: J
authors.lastname: Léonil
authors.forename: Gheorge
authors.initials: G
authors.lastname: Airinei
authors.forename: Catherine
authors.initials: C
authors.lastname: Luengo
authors.forename: Sophie
authors.initials: S
authors.lastname: Daré
authors.forename: Robert
authors.initials: R
authors.lastname: Benamouzig
authors.forename: Hélène
authors.initials: H
authors.lastname: Fouillet
authors.forename: Jacques
authors.initials: J
authors.lastname: Fauquant
authors.forename: Daniel
authors.initials: D
authors.lastname: Tomé
authors.forename: Claire
authors.initials: C
authors.lastname: Gaudichon
mesh_terms: 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
chemical_list: D000596:Amino Acids; D002364:Caseins; D008894:Milk Proteins; D009587:Nitrogen Isotopes; D002245:Carbon Dioxide; D014508:Urea