Metabolic availability of amino acids in food proteins: new methodology.

Abstract

Abstract Protein quality is a term used to describe the capacity of food proteins to meet the amino acid requirement estimates for humans. It is a measure of the nutritional value of food protein sources which depends on the concentration and balance of amino acids and on the digestibility and availability of the food protein for metabolic processes. However, not all foods are equal in their capacity to supply protein and amino acids. The protein digestibility-corrected amino acid score (PDCAAS) was proposed as the method of choice for assessing protein quality in humans. Although it is an improvement over previous methods, the digestibility correction factor used to calculate PDCAAS is based on a rat fecal digestibility model and thus does not account for losses associated with incomplete digestion and absorption, gut endogenous amino acid losses, or absorbed amino acids which are unavailable due to the effect of heat processing and anti-nutritional factors on protein quality. Metabolic availability is a new method for protein quality evaluation utilizing the indicator amino acid oxidation technique. Oxidation of the indicator amino acid is inversely proportional to whole body protein synthesis, and responds rapidly to changes in the bioavailability of amino acids for metabolic processes, and therefore reflects the true metabolic availability (MA) of amino acids. MA is minimally invasive, determined directly in humans, and is based on minimal assumptions which have been validated in animals. It can be used to assess all protein sources, measures the bioavailability of individual amino acids and can be routinely applied in humans. Studies in animals and humans have demonstrated that MA provides an accurate estimate of the protein quality from various protein sources. Practical application of the MA method has the potential to significantly advance protein quality evaluation in humans.