Starch

Starch is the main form of complex carbohydrate in dry pet food, a glucose polymer drawn from cereals, legumes, potato or other tubers. It does double duty: it supplies energy, and it is the structural glue that lets a kibble hold its shape. The key process is gelatinisation. During extrusion, heat, moisture and pressure break open the starch granules, which makes them far more accessible to digestive enzymes and dramatically raises [digestibility](/glossary/digestibility). Well-cooked starch is digested efficiently by dogs. The cat, an obligate carnivore, handles well-cooked starch adequately but has a more limited capacity for large carbohydrate loads, which is one reason feline diets tend to lean more on protein and fat. The source matters too: legumes and sorghum tend to produce a lower [glycaemic index](/glossary/glycaemic-index) response than potato or white rice. A surprising twist comes after cooking: when cooked starch cools, a fraction recrystallises into resistant starch, which escapes digestion in the small intestine and behaves like a fermentable [fibre](/glossary/fibre) in the colon, feeding beneficial bacteria. On a label, starch is usually implied rather than stated, appearing through ingredients such as rice, maize or pea, and reflected indirectly in the carbohydrate calculated by difference. See the [Petipedia glossary](/glossary) for related carbohydrate terms.

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