The proportion of a foodstuff absorbed from the digestive tract into the bloodstream, normally 90-95%. It is measured as the difference between intake and faecal output, with allowance being made for that part of the faeces that is not derived from undigested food residues (shed cells of the intestinal tract, bacteria, residues of digestive juices).
The proportion of a food component utilized by the body; it is measured as the difference between the quantity consumed and that excreted, expressed as a percentage of the quantity consumed.