Postprandial modulation of dietary and whole-body nitrogen utilization by carbohydrates in humans.
BACKGROUND
Sucrose exerts a sparing effect on whole-body protein metabolism, mainly during the absorptive phase.


OBJECTIVE
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.


METHODS
Twenty-one subjects equipped with ileal tubes ingested (15)N-labeled soy protein combined with [(13)C]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 (13)CO(2) enrichment in breath and (15)N enrichment in plasma amino acids. Deamination of dietary and endogenous amino acid was determined from body urea, urinary nitrogen, and (15)N enrichment.


RESULTS
(13)CO(2) recovery in breath and (15)N plasma amino acid enrichments were highly correlated (R:(2) >/= 0.95, P: < 0.001, for both meals) and markedly delayed by sucrose (half-(13)CO(2) 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.


CONCLUSIONS
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.
Mariotti
F
F
UMR INRA, Institut National Agronomique Paris-Grignon, Unité de Physiologie de la Nutrition et du Comportement Alimentaire, Paris, France.
Mahé
S
S
Luengo
C
C
Benamouzig
R
R
Tomé
D
D
D000328:Adult; D000596:Amino Acids / Q000097:blood / Q000378:metabolism / Q000652:urine; D000641:Ammonia / Q000097:blood / Q000652:urine; D001786:Blood Glucose / Q000032:analysis; D002245:Carbon Dioxide / Q000032:analysis; D004396:Coloring Agents / Q000032:analysis; D003404:Creatinine / Q000097:blood; D003641:Deamination; D004044:Dietary Proteins / Q000378:metabolism*; D019422:Dietary Sucrose / Q000378:metabolism*; D005260:Female; D005766:Gastrointestinal Contents / Q000737:chemistry*; D006801:Humans; D007082:Ileum / Q000502:physiology; D007328:Insulin / Q000032:analysis; D008297:Male; D009584:Nitrogen / Q000032:analysis / Q000378:metabolism*; D010637:Phenolsulfonphthalein / Q000032:analysis; D011092:Polyethylene Glycols / Q000032:analysis; D019518:Postprandial Period; D012997:Solvents / Q000032:analysis; D030262:Soybean Proteins / Q000378:metabolism; D014508:Urea / Q000097:blood / Q000652:urine
D000596:Amino Acids; D001786:Blood Glucose; D004396:Coloring Agents; D004044:Dietary Proteins; D019422:Dietary Sucrose; D007328:Insulin; D012997:Solvents; D030262:Soybean Proteins; D002245:Carbon Dioxide; D011092:Polyethylene Glycols; D000641:Ammonia; D014508:Urea; D003404:Creatinine; D010637:Phenolsulfonphthalein; D009584:Nitrogen