Crude fibre

Crude fibre (US: crude fiber) is the plant-fibre fraction of a food as measured by a conventional, decades-old laboratory method, and its single most important property is that it understates the true total dietary fibre present. The technique recovers mainly the insoluble, structural fibre such as cellulose and lignin, while losing much of the soluble fibre, so the value declared in a [guaranteed analysis](/glossary/guaranteed-analysis) or [analytical constituents](/glossary/analytical-constituents) list can be considerably lower than the food's real fibre load (FEDIAF, 2024). This matters for premium buyers in a specific way: fibre is functionally important in several diets, from weight-management and [light formulas](/glossary/light-diet) where it supports satiety, to feline [indoor diets](/glossary/indoor-diet) where it helps limit hairball formation, yet the printed crude fibre number does not fully capture that contribution. A practical consequence is that two foods with the same low crude fibre figure can differ markedly in how they actually behave in the gut, because their soluble fibre, which the test largely misses, differs. Crude fibre also enters the [NFE carbohydrate estimate](/glossary/carbohydrate-estimate-nfe), so its imprecision propagates into that calculation as well. The take-home is to treat the number as a rough lower bound rather than a complete picture of fibre, and to weigh it alongside the diet's stated purpose. For more on what label values do and do not tell you, see the [Petipedia glossary](/glossary).

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