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HEALTH

The Claim

Under normal conditions, only a very small fraction of dietary amino acids in the small-intestinal lumen are diverted by other substances or are consumed by colonic bacteria before being absorbed, so amino-acid loss is very low.

Verified by Lenz ·

The Short Version

Most dietary amino acids are absorbed in the small intestine under normal, healthy conditions, so losses before absorption are generally low. Human studies and reviews commonly report ileal amino-acid digestibility above 90%, often above 95%. The wording is somewhat broad because digestibility differs by protein source and some proteinaceous material still reaches the colon, but that does not overturn the main conclusion for typical diets.

Caveats

  • Digestibility is not uniform: some proteins and processing conditions produce substantially lower amino-acid absorption than typical mixed diets.
  • Proteinaceous material reaching the colon is not all unabsorbed dietary amino acids; a meaningful share is endogenous nitrogen from enzymes, mucus, and sloughed cells.
  • The claim is limited to normal physiology in healthy people and should not be generalized to bowel disease, malabsorption, or unusual diets.

The Receipts

  1. Amino Acid Absorption in the Large Intestine of Humans

    PubMed

  2. Mammalian colonic contribution of amino acids to whole-body homeostasis

    PubMed

  3. True Ileal Amino Acid Digestibility and Protein Quality of 15N–Labeled Faba Bean Protein in Humans

    PubMed Central (American Journal of Clinical Nutrition)

  4. Comparison of True Ileal Amino Acid Digestibility between Adult Humans and Growing Pigs

    Journal of Nutrition (via University of Illinois)

  5. The role of colonic microbiota amino acid metabolism in gut health and disease

    Frontiers in Nutrition (via PubMed Central)

  6. Protein and amino acid digestibility: definitions and conventional oro-ileal balance approaches

    Frontiers in Nutrition

  7. True Ileal Amino Acid Digestibility and Protein Quality of 15N-Labeled Faba Bean Protein in Humans

    PubMed

  8. Whole-body nitrogen and amino acid metabolism in humans

    European Journal of Clinical Nutrition (Nature)

  9. Potential Implications for Amino Acid Bioavailability: Lessons from Ileal Amino Acid Digestibility Studies in Humans and Other Monogastric Animals

    Frontiers in Nutrition (via PubMed Central)

  10. The kinetics of amino acid disappearance in the small intestine is not affected by correction for amino acids released into the hindgut

    British Journal of Nutrition (via PubMed Central)

+ 13 more sources — see the full list on Lenz

Filed Under

Amino AcidsColonColonic BacteriaSmall Intestine

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