NUTRIENT BIOAVAILABILITY. The chemical analysis of a food gives us values for the total amounts of particular nutrients that are present. Commonly, when a food is to be analyzed, it is first treated with a strong acid, or an enzyme, that breaks up complex materials into simpler, soluble products. Thus, the starch content of a food may be measured as the amount of additional sugar found after the treatment of the food with an enzyme that acts specifically on starch, and nothing else, to break the large molecules down to glucose. Usually, if different analytical methods are compared, the one giving the highest values is chosen, on the grounds that it has extracted the nutrient in question most completely.

However, from a nutritional point of view our interest is in how much our digestive system will be able to extract in a form that can be absorbed into the bloodstream. The term "digestibility" was formerly used to...