Digestibility

Digestibility is the proportion of a nutrient, or of the whole food, that the animal actually absorbs rather than passing in the faeces. It is expressed as a percentage: a protein with 90 percent digestibility means nine-tenths of it is taken up and only one-tenth is lost. Digestibility is what separates a high figure on the label from real nutritional value, because [crude protein](/glossary/crude-protein) tells you how much protein is present but not how much the animal can use. A premium animal-protein source is typically far more digestible than poorly processed material, and overcooking can actually reduce protein quality through the Maillard reaction, which binds [lysine](/glossary/lysine) and makes it unavailable. Two foods with identical analytical constituents can perform very differently if one is more digestible. Higher digestibility also means smaller, firmer stools and less waste, a practical marker owners can observe at home. Digestibility feeds directly into [energy density](/glossary/energy-density), since only the digestible fraction provides usable energy, and into how portions are calculated. Cats and dogs differ somewhat: cats are highly efficient at digesting animal protein and fat but less so at large starch loads. Manufacturers measure digestibility in feeding trials, though it is rarely printed on the pack. See the [Petipedia glossary](/glossary) for related quality measures.

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General documentary information. For an individual animal, a veterinarian's advice takes precedence over any online content.