Postprandial modulation of dietary and whole-body nitrogen utilization by carbohydrates in humans12

• Published in: The American journal of clinical nutrition Vol. 72; no. 4; pp. 954 - 962
• Main Authors: Mariotti, François, Mahé, Sylvain, Luengo, Catherine, Benamouzig, Robert, Tomé, Daniel
• Format: Journal Article
• Language: English
• Published: Elsevier Inc 01.10.2000
• Subjects: Adults; amino acids; carbon isotopes; dietary carbohydrate; dietary protein; gastric emptying; intestinal absorption; nitrogen isotopes; nitrogen metabolism; oxidation; pharmacokinetics; protein metabolism; sucrose; protein metabolism; amino acids; nitrogen metabolism; oxidation; sucrose; gastric emptying; nitrogen isotopes; dietary carbohydrate; pharmacokinetics; Adults; intestinal absorption; dietary protein; carbon isotopes
• ISSN: 0002-9165
• DOI: 10.1093/ajcn/72.4.954

Sucrose exerts a sparing effect on whole-body protein metabolism, mainly during the absorptive phase. We aimed to characterize the acute postprandial effect of addition of sucrose on deamination of dietary and endogenous nitrogen, with particular consideration being given to the effects of bioavailability. Twenty-one subjects equipped with ileal tubes ingested 15N-labeled soy protein combined with [13C]glycine, with (n = 10) or without (n = 11) sucrose. Dietary and endogenous ileal flow of nitrogen were determined from the ileal effluents. The kinetics of dietary amino acid transfer to the blood were characterized by 13CO2 enrichment in breath and 15N enrichment in plasma amino acids. Deamination of dietary and endogenous amino acid was determined from body urea, urinary nitrogen, and 15N enrichment. 13CO2 recovery in breath and 15N plasma amino acid enrichments were highly correlated (R2 ≥ 0.95, P < 0.001, for both meals) and markedly delayed by sucrose (half-13CO2 recovery: 274 min compared with 167 min), whereas exogenous and endogenous ileal nitrogen kinetics and balances remained unchanged. Addition of sucrose halved the early (0–2 h) deamination peak of dietary nitrogen and reduced endogenous nitrogen oxidation over the first 4 h. Both were reduced by 18–24% over the 8-h period after the meal. Without changing the nitrogen absorptive balance, sucrose markedly affected the bioavailability profile, which is governed by gastric emptying. Endogenous and dietary nitrogen were not spared in the same way and over the same periods, showing that the metabolism of endogenous and dietary nitrogen may be affected differently by nutritional modulation, even if the effects are of a similar magnitude over the entire postprandial period.