title: Mechanism governing short-term fed-state adaptation to dietary protein restriction.
abstract: The mechanism governing short-term adaptation to dietary protein restriction was investigated in nine normal adults by measuring their metabolic response to a standard mixed meal, first while they were adapted to a conventional, high-protein diet (day 1) and then again after they had eaten two low-protein meals (day 2). Urea appearance (measured as the sum of its urinary excretion and the change in body urea pool size), body retention of 15N-alanine included in each test meal, and whole-body protein turnover were calculated over the 9 hours following meal consumption on each day. Postprandial urea nitrogen appearance was 5.05 +/- 0.26 g/9 h on day 1 and decreased to 4.16 +/- 0.31 on day 2 (P < .05). Whole-body N flux (Q), protein synthesis (S), and protein breakdown (B) all decreased significantly on day 2 as assessed using either urea or ammonium end-product enrichments; however, recovery of 15N in the test meal as 15N-urea was similar on both days, approximately 22%. It is concluded that short-term metabolic adaptation occurs within two meals of reduced protein intake. The mechanism appears not to involve selectively an increased "first-pass" retention of dietary amino acids, but rather a general reduction in fed-state whole-body protein breakdown.
authors.affiliation: McGill Nutrition and Food Science Centre, McGill University, Montreal, Quebec, Canada.
authors.forename: A
authors.initials: A
authors.lastname: Taveroff
authors.forename: H
authors.initials: H
authors.lastname: Lapin
authors.forename: L J
authors.initials: LJ
authors.lastname: Hoffer
mesh_terms: D000222:Adaptation, Physiological / Q000502:physiology*; D000328:Adult; D000409:Alanine / Q000032:analysis / Q000378:metabolism; D000596:Amino Acids / Q000097:blood; D001786:Blood Glucose / Q000032:analysis; D002940:Circadian Rhythm / Q000502:physiology; D003404:Creatinine / Q000652:urine; D004038:Diet, Reducing; D004044:Dietary Proteins / Q000008:administration & dosage*; D005260:Female; D008401:Gas Chromatography-Mass Spectrometry; D005934:Glucagon / Q000097:blood; D006801:Humans; D007328:Insulin / Q000097:blood; D008297:Male; D009587:Nitrogen Isotopes; D013997:Time Factors; D014508:Urea / Q000097:blood / Q000652:urine
chemical_list: D000596:Amino Acids; D001786:Blood Glucose; D004044:Dietary Proteins; D007328:Insulin; D009587:Nitrogen Isotopes; D014508:Urea; D005934:Glucagon; D003404:Creatinine; D000409:Alanine