Amino Acid Absorption and Subsequent Muscle Protein Accretion Following Graded Intakes of Whey Protein in Elderly Men

Am J Physiol Endocrinol Metab. 2012 Apr 15;302(8):E992-9. doi: 10.1152/ajpendo.00517.2011. Epub 2012 Feb 14.

Abstract

Whey protein ingestion has been shown to effectively stimulate postprandial muscle protein accretion in older adults. However, the impact of the amount of whey protein ingested on protein digestion and absorption kinetics, whole body protein balance, and postprandial muscle protein accretion remains to be established. We aimed to fill this gap by including 33 healthy, older men (73 ± 2 yr) who were randomly assigned to ingest 10, 20, or 35 g of intrinsically l-[1-¹³C]phenylalanine-labeled whey protein (n = 11/treatment). Ingestion of labeled whey protein was combined with continuous intravenous l-[ring-²H₅]phenylalanine and l-[ring-²H₂]tyrosine infusion to assess the metabolic fate of whey protein-derived amino acids. Dietary protein digestion and absorption rapidly increased following ingestion of 10, 20, and 35 g whey protein, with the lowest and highest (peak) values observed following 10 and 35 g, respectively (P < 0.05). Whole body net protein balance was positive in all groups (19 ± 1, 37 ± 2, and 58 ± 2 μmol/kg), with the lowest and highest values observed following ingestion of 10 and 35 g, respectively (P < 0.05). Postprandial muscle protein accretion, assessed by l-[1-¹³C]phenylalanine incorporation in muscle protein, was higher following ingestion of 35 g when compared with 10 (P < 0.01) or 20 (P < 0.05) g. We conclude that ingestion of 35 g whey protein results in greater amino acid absorption and subsequent stimulation of de novo muscle protein synthesis compared with the ingestion of 10 or 20 g whey protein in healthy, older men.

Trial registration: ClinicalTrials.gov NCT00557388.

Publication types

  • Comparative Study
  • Randomized Controlled Trial

MeSH terms

  • Aged
  • Aging / metabolism*
  • Algorithms
  • Amino Acids / blood
  • Amino Acids / metabolism*
  • Blood Glucose
  • Carbon Isotopes
  • Deuterium
  • Digestion
  • Humans
  • Insulin / blood
  • Intestinal Absorption*
  • Kinetics
  • Male
  • Milk Proteins / administration & dosage
  • Milk Proteins / metabolism*
  • Muscle Proteins / biosynthesis*
  • Oxidation-Reduction
  • Phenylalanine / blood
  • Phenylalanine / metabolism
  • Postprandial Period
  • Quadriceps Muscle / metabolism*
  • Tyrosine / blood
  • Tyrosine / metabolism
  • Whey Proteins

Substances

  • Amino Acids
  • Blood Glucose
  • Carbon Isotopes
  • Insulin
  • Milk Proteins
  • Muscle Proteins
  • Whey Proteins
  • Tyrosine
  • Phenylalanine
  • Deuterium

Associated data

  • ClinicalTrials.gov/NCT00557388