Digestible means possible to digest — capable of being broken down by the digestive system into absorbable nutrients. Digestibility is a spectrum, not a switch: simple starches and sugars are almost completely digestible, proteins mostly so, while cellulose fibre passes through untouched and some starches resist digestion depending on cooking and structure. Food scientists measure it precisely — apparent versus true digestibility, corrected for the body’s own losses — because the number decides how much energy and protein a food actually delivers, not just what the analysis says it contains. Processing shifts digestibility both ways: cooking gelatinises starch and denatures protein, raising it; excessive heat damage or heavy fibre can lower it. For infant formula, animal feed, and therapeutic diets, digestibility is a primary quality criterion.