title: Factors affecting plasma amino acid concentrations in control subjects.
abstract: Plasma amino acid concentrations were determined in groups of normal control subjects under fasting and postprandial conditions. Differences were observed that were found to be, to a considerable extent, sex-related. Fasting females had lower concentrations than fasting males of several amino acids, although postprandial differences in concentrations between the sexes were not significant. Under the dietary conditions normal for a British population, no significant diurnal variation of plasma amino acid concentrations was found. Reducing the dietary protein by 30% failed to affect plasma amino acid concentrations; however, increasing the dietary protein by 50% resulted in a significant increase in the plasma concentrations of several amino acids, and induced a significant degree of variation throughout the day in six, proline, half-cystine, methionine, valine, leucine, and isoleucine. The importance of these results with regard to the interpretation of population mean values and disease diagnosis is discussed.
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000596:Amino Acids / Q000097:blood*; D002940:Circadian Rhythm; D003553:Cystine / Q000097:blood; D004044:Dietary Proteins / Q000008:administration & dosage*; D004435:Eating; D005215:Fasting; D005260:Female; D006801:Humans; D007532:Isoleucine / Q000097:blood; D007930:Leucine / Q000097:blood; D008297:Male; D008715:Methionine / Q000097:blood; D008875:Middle Aged; D011392:Proline / Q000097:blood; D012737:Sex Factors; D014633:Valine / Q000097:blood
chemical_list: D000596:Amino Acids; D004044:Dietary Proteins; D007532:Isoleucine; D003553:Cystine; D011392:Proline; D008715:Methionine; D007930:Leucine; D014633:Valine