Gastroenterology

Gastroenterology

Volume 123, Issue 1, July 2002, Pages 50-59
Gastroenterology

Clinical–Alimentary Tract
Ileal losses of nitrogen and amino acids in humans and their importance to the assessment of amino acid requirements,☆☆,

https://doi.org/10.1053/gast.2002.34233 Get rights and content

Abstract

Background & Aims: Irreversible amino acid losses at the human ileum are not taken into account when tracer-derived amino acid requirements are calculated because the data available are scarce. We have investigated amino acid losses at the ileal level in humans after ingestion of a protein meal. Methods: Thirteen volunteers ingested a single meal of 15N milk or soy proteins. The appearance of 15N and 15N amino acids in the ileal effluents collected using an ileal tube was monitored for 8 hours. Results: In the soy group, higher losses of endogenous nitrogen, especially originating from amino acids, were observed, as well as a higher flow rate of dietary non–amino acid nitrogen. With soy protein, the digestibilities of valine, threonine, histidine, tyrosine, alanine, and proline were significantly lower than with milk. Ileal losses of leucine, valine, and isoleucine amounted to 12, 10, and 7 mg · kg−1 · day−1, respectively. Threonine ileal loss (9–12 mg · kg−1 · day−1) was particularly high compared with the current amino acid requirement. Conclusions: Amino acid losses at the human terminal ileum are substantial and depend on the type of dietary protein ingested. Although it remains unclear whether intact amino acids are absorbed in the colon, we suggest that ileal losses should be considered an important component of amino acid requirements.

GASTROENTEROLOGY 2002;123:50-59

Section snippets

Experimental meals

We compared 2 different purified protein test meals, fed to the subjects on the morning of the experimental day: a milk protein meal (295 mmol N) and a soy protein meal (316 mmol N), providing 502 kJ. The meals consisted of 30 g of milk or soy protein isolate stirred into water to obtain a final volume of 500 mL. Dietary protein purification and 15N labeling of milk and soy were performed as described in our previous studies.16, 17, 22 Briefly, milk was obtained from a lactating cow given

Endogenous and dietary nitrogen in the ileal effluents

The flow rate of endogenous nitrogen and the cumulative appearance of dietary nitrogen in the ileal effluents are shown in Figure 1.

. (A) Endogenous nitrogen flux in human ileal effluents after ingestion of milk or soy protein. (B) Cumulative dietary nitrogen appearance in human ileal effluents after the ingestion of milk or soy protein. Values are mean ± SD. Asterisks indicate significant differences between groups. (Repeated-measures ANOVA, P < 0.05.)

The endogenous flow rate was enhanced during

Discussion

The present study allowed further characterization of nitrogen compounds in ileal intestinal effluents in humans. To the best of our knowledge, this study also provides the first data on individual amino acid losses of both endogenous and dietary origin in healthy human subjects. We demonstrated that an IAA amount corresponding to 40%–100% of current IAA requirements20 is recovered at the terminal ileum and thus should be considered when estimating IAA requirements.

Acknowledgements

The authors thank ARILAIT Recherches for their comments on the manuscript and the staff of the DIfE Protein Metabolism Unit for the excellent technical assistance with 15N gas chromatography-combustion-isotope ratio mass spectrometry measurements.

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    Address requests for reprints to: Claire Gaudichon, Ph.D., Institut National Agronomique Paris-Grignon (INA PG), Unité de Physiologie de la Nutrition et du Comportement Alimentaire, 16 Rue Claude Bernard, 75005 Paris, France. e-mail: [email protected] ; fax: (33) 1-44-08-18-25.

    ☆☆

    Supported by grants from ARILAIT Recherches (Paris, France), PROCOPE grants from the Deutsche Akademische Austauschdienst (Bonn, Germany), and the French Ministry for Foreign Affairs (Paris, France).

    Dr. Metges is currently affiliated with the Research Institute for the Biology of Farm Animals, Dummerstorf, Germany.

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