The British journal of nutrition
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Available amino acids are those absorbed from the gastrointestinal tract in a form suitable for body protein synthesis. True ileal digestible amino acids are determined based on the difference between dietary amino acid intake and unabsorbed dietary amino acids at the terminal ileum. The accuracy of ileal digestible amino acid estimates for predicting available amino acid content depends on several factors, including the accuracy of the amino acid analysis procedure. ⋯ Consequently, methionine and cysteine are overestimated if methionine sulphone or cysteic acid are present in the original material. Overall, given the problems associated with the analysis of some amino acids in processed foodstuffs, the available amino acid content may not always be accurately predicted by true ileal amino acid digestibility estimates. For such amino acids specific analytical strategies may be required.
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To meet the protein and amino acid requirements of individuals and of populations requires information not only about their requirements but also about the capacity of available foods to meet those requirements. Most of our current knowledge of the digestibility of food proteins and the methods to estimate it has been derived from work with animals. Because the microbiota of the large intestine alter the amino acid composition of the digesta, and because only trivial quantities of amino acids are absorbed intact from the large intestine, the current method of choice for assessing amino acid digestibility is ileal digestibility corrected for basal endogenous losses, that is, standardized ileal digestibility. ⋯ Microbial activity in the gastrointestinal (GI) tract is not confined to the large intestine: the numbers and metabolic activity of the upper GI microbiota lead to substantial amounts of microbial protein leaving the ileum. It appears however that a large proportion of the amino acids used by the upper GI microbiota are preformed - from the diet or from endogenous materials - rather than from de novo synthesis. Although there are still uncertainties about the impact of microbial activity in the upper GI tract, the amino acid composition of ileal digesta provides the best available basis for estimating the proportion of dietary amino acids available for metabolism.
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Trans-fatty acids (TFA) have adverse effects on blood lipids, but whether TFA from different sources are associated with risk of CVD remains unresolved. The objective of the present study was to evaluate the association between TFA intake from partially hydrogenated vegetable oils (PHVO), partially hydrogenated fish oils (PHFO) and ruminant fat (rTFA) and risks of death of CVD, CHD, cerebrovascular diseases and sudden death in the Norwegian Counties Study, a population-based cohort study. Between 1974 and 1988, participants were examined for up to three times. ⋯ These associations with rTFA intake were not significant in men (P interaction ≥ 0.01). The present study supports that TFA intake, irrespective of source, increases CVD risk. Whether TFA from PHVO decreases risk of cerebrovascular diseases warrants further investigation.
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Cereals and legumes are staple foods in India and are limiting in lysine and sulphur amino acids, respectively. Available lysine loss, due to Maillard-type reactions that may occur during food preparation, exacerbates the problem of lysine deficiency particularly in cereals. Consequently, determining the contents of digestible essential amino acids, particularly lysine, is important. ⋯ True ileal amino acid digestibility varied widely both across ingredients and prepared foods for each amino acid (on average 60-92 %) and across amino acids within each ingredient and prepared food (overall digestibility 31-96 %). Amino acid digestibility was low for many of the ingredients and prepared foods and consequently digestibility must be considered when assessing the protein quality of poorer quality foods. Given commonly encountered daily energy intakes for members of the Indian population, it is estimated that lysine is limiting for adults in many Indian diets.
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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. ⋯ 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.