Gut luminal endogenous protein: Implications for the determination of ileal amino acid digestibility in humans

Abstract

The true ileal digestibility assay provides the most informative measure of digestibility to assess bioavailability of amino acids in foods for humans. To determine 'true' estimates of ileal amino acid digestibility, requires that endogenous amino acids present in digesta at the terminal ileum be quantified. The amounts of endogenous amino acids in ileal digesta can be determined after feeding an animal or human a protein-free diet (traditional approach) or by various methods after giving a protein-containing diet. When the protein-free method has been applied with adult human subjects an overall mean value (three separate studies) for endogenous ileal nitrogen flow of 800 mg N/d has been reported. This value is considerably lower than a comparable value obtained after feeding protein of 1852 mg N/d (mean of four separate studies), and thus endogenous ileal N and amino acids should be measured under conditions of protein alimentation. There is some confusion concerning the terminology used to define digestibility, with the term "true" digestibility having different adopted meanings. Here, true amino acid digestibility is defined as apparent amino acid digestibility corrected for the basal amino acid losses determined after giving either a protein-free or a protein-containing diet. Basal losses should be determined at a defined dry-matter and protein intake. The protein-free diet approach to determining endogenous amino acids is considered unphysiological and basal losses refer to ileal endogenous amino acid flows associated with digesta dry-matter flow, and not including "specific" effects of dietary factors such as non starch polysaccharides and anti nutritional factors. Arguments are advanced that the enzyme hydrolysed protein/ultra filtration method may be suitable for routine application with a cannulated pig model, to obtain physiologically-valid basal estimates of ileal endogenous amino acids to allow calculation of true ileal amino acid digestibility in the pig, and then prediction (via statistical relationships) of true coefficients of amino acid digestibility in humans.

A növényi alapú étrendről

“…Az emberi szervezet esetén a száj felől a terminális ileum irányába naponta 90 grammnyi mennyiségű fehérje áramlik át, amelynek jelentős része újrahasznosul [24]. …”

Dietary Protein Structure Affects Endogenous Ileal Amino Acids But Not True Ileal Amino Acid Digestibility in Growing Male Rats

“…Nondietary protein found as part of the digesta at the terminal ileum comprises endogenous proteins secreted into the gut lumen, sloughed gut epithelial cells, and microbial bodies (1)(2)(3)(4). This flow of material, often collectively referred to as the endogenous protein flow, is of fundamental interest because it reflects gut metabolism and is a measure used to adjust apparent estimates of ileal protein and amino acid digestibility.…”

“…This flow of material, often collectively referred to as the endogenous protein flow, is of fundamental interest because it reflects gut metabolism and is a measure used to adjust apparent estimates of ileal protein and amino acid digestibility. The total endogenous ileal amino acids (EIAAs) 4 from the upper digestive tract can be considered in 2 parts: 1) basal and 2) specific. Basal EIAAs are defined as the endogenous amino acids found in terminal ileal digesta related to food dry matter (DM) flow, whereas the variable component, the specific losses, are the endogenous amino acids found in terminal ileal digesta related to the effects of specific dietary components, such as fiber or antinutritional factors (ANFs) (5).…”

Endogenous proteins in terminal ileal digesta of adult subjects fed a casein-based diet

“…Protein of the microbiota that normally inhabit the GIT, although not strictly of endogenous origin (but nondietary), is also expected to make a significant contribution to the protein losses (6). Residual amounts of exogenous and endogenous proteinaceous material that remain unabsorbed at the terminal ileum are considered to have little nutritional value (7) because amino acid absorption in the large intestine is thought to be minimal (8,9).…”

“…Accurate determinations of endogenous total nitrogen and amino acid flows are necessary to allow the determination of true dietary amino acid digestibility coefficients and for the factorial estimation of dietary amino acid requirements (15). Although there have been several published estimates of the endogenous amino acid composition of human ileal digesta (8), to our knowledge, there have been no systematic studies of the endogenous protein composition (ie, sources of endogenous protein) of ileal digesta in humans. Such a study has been recently undertaken in the growing pig (16).…”