title: Inverse relationship between protein intake and plasma free amino acids in healthy men at physical exercise.
abstract: The effect of a "normal" (n = 8) and "high" (n = 6) protein intake (1 and 2.5 g x kg(-1) x day(-1), respectively) and of exercise on plasma amino acid (AA) concentrations, insulin, and glucagon concentrations was followed throughout a continuous 24-h period in adult male subjects at energy balance after six days on a standardized diet and exercise program. Subjects were fasting from 2100 on day 6 to 1200 on day 7 and then fed 10 identical meals hourly until 2100. Physical exercise was performed (46% maximal oxygen uptake) between 0830 and 1000 (fasting) and in a fed state (1600-1730) on each day. The normal-protein group showed fasting plasma AA concentrations that were higher (P < 0.05) than those for the high-protein group, except for leucine, methionine, and tyrosine. Glutamine, glycine, alanine, taurine, and threonine concentrations were distinctly higher ( approximately 30% or greater) throughout the 24-h period in subjects consuming the normal- vs. the high-protein diets. Exercise appeared to increase, although not profoundly, the plasma concentrations of amino acids except for glutamate, histidine, ornithine, and tryptophan. The profound diet-related differences in plasma AA concentrations are only partially explained by differences in the renal clearance of the amino acids. We speculate on the possible metabolic basis for these findings.
authors.affiliation: Department of Medical Sciences, Nutrition and Clinical Chemistry, Uppsala University, SE-75237 Uppsala, Sweden.
authors.forename: A H
authors.initials: AH
authors.lastname: Forslund
authors.forename: L
authors.initials: L
authors.lastname: Hambraeus
authors.forename: H
authors.initials: H
authors.lastname: van Beurden
authors.forename: U
authors.initials: U
authors.lastname: Holmbäck
authors.forename: A E
authors.initials: AE
authors.lastname: El-Khoury
authors.forename: G
authors.initials: G
authors.lastname: Hjorth
authors.forename: R
authors.initials: R
authors.lastname: Olsson
authors.forename: M
authors.initials: M
authors.lastname: Stridsberg
authors.forename: L
authors.initials: L
authors.lastname: Wide
authors.forename: T
authors.initials: T
authors.lastname: Akerfeldt
authors.forename: M
authors.initials: M
authors.lastname: Regan
authors.forename: V R
authors.initials: VR
authors.lastname: Young
mesh_terms: D000328:Adult; D000596:Amino Acids / Q000097:blood*; D002940:Circadian Rhythm; D004044:Dietary Proteins / Q000008:administration & dosage*; D004734:Energy Metabolism; D015444:Exercise / Q000502:physiology*; D005215:Fasting; D005502:Food; D005934:Glucagon / Q000097:blood; D006801:Humans; D007328:Insulin / Q000097:blood; D007668:Kidney / Q000378:metabolism; D008297:Male
chemical_list: D000596:Amino Acids; D004044:Dietary Proteins; D007328:Insulin; D005934:Glucagon