Proteins are essential for body structure and growth, for regulating organ and tissue function and for protecting against infection. Protein quality is defined based on the capacity of a protein source to provide adequate amounts of essential amino acids.?

Protein Quality
It is difficult to measure the proportion of essential amino acids absorbed from a given diet without taking a sample of ingested food from the gastrointestinal tract. However, this approach is not only invasive, but is prone to error related to protein digestion by bacteria in the large intestines.
A dual tracer stable isotope technique, based on labelling of food with both deuterium and 13C-protein/crystalline amino acid, enables a non-invasive and accurate assessment of the digestion and absorption of protein from the diet. ?
This isotope technique can be used to generate information on true protein digestion which can aid discussions on recommendations for protein intake and requirements.