Postprandial oxidative losses of free and protein-bound amino acids in the diet: interactions and adaptation.
Postprandial oxidation of dietary free amino acids or egg white protein was studied using the [13CO2] breath test in rats, as well as in humans. Thirty-eight male rats were assigned to four dietary test groups. Two diets only differed in their protein fraction. Diet I contained 21% egg white protein. For the breath test egg white protein, intrinsically labelled with [1-13C]-leucine, was used as a substrate. Diet II contained the same amino acids as diet I, though not as egg white protein but in free form. Free [1-13C]-leucine was used to label this diet. In addition, two 1:1 mixtures of both diets were used. During the breath test either the free amino acid or the protein fraction was labelled as in diets I or II. The animals were breath-tested following short-term (day 5) and long-term adaptation (day 20) to their experimental diet. For all diets, including the mixed diets, postprandial oxidative losses on day 5 were significantly higher for the free leucine compared with the protein-derived leucine. Differences between free and protein-derived leucine oxidation had, however, largely disappeared on day 20. The human subjects were breath-tested without any adaptation period to the diets. The oxidative losses of free leucine were also higher than those of protein-derived leucine. None of the studies showed any indication for an interaction between the oxidation of protein-derived amino acids and free amino acids. It is concluded that free and protein-derived amino acids in the diet are mainly metabolized independently.
Nolles
J A
JA
Human and Animal Physiology Group, Wageningen University, Wageningen, The Netherlands. jelmer.nolles@wur.nl
Verreijen
A M
AM
Koopmanschap
R E
RE
Verstegen
M W A
MW
Schreurs
V V A M
VV
D000222:Adaptation, Physiological / Q000502:physiology*; D000596:Amino Acids / Q000378:metabolism*; D000818:Animals; D001944:Breath Tests; D002245:Carbon Dioxide / Q000378:metabolism; D004032:Diet; D005260:Female; D006801:Humans; D008297:Male; D010084:Oxidation-Reduction; D019518:Postprandial Period / Q000502:physiology*; D051381:Rats; D017208:Rats, Wistar; D013997:Time Factors; D055815:Young Adult
D000596:Amino Acids; D002245:Carbon Dioxide