Calcium-to-phosphorus ratio

The calcium-to-phosphorus ratio is the proportion of [calcium](/glossary/calcium) to [phosphorus](/glossary/phosphorus) in a diet, and it matters as much as the absolute amount of either mineral, especially during growth. Both minerals are needed to build the skeleton, but they must arrive in balance: the generally accepted target sits between about 1:1 and 2:1 calcium to phosphorus for most diets (FEDIAF, 2021). Get it wrong and bone development suffers. Too little calcium relative to phosphorus, the classic risk of an all-meat home diet, can trigger nutritional secondary hyperparathyroidism, in which the body leaches calcium from the bones to keep blood levels stable, leaving the skeleton fragile. Excess calcium is just as harmful in the other direction, particularly for large and giant-breed puppies, where it is linked to developmental skeletal disease. This is why large-breed puppy foods are formulated with a tightly controlled ratio and a capped calcium maximum. Cats are less commonly affected by ratio problems than fast-growing large-breed dogs, but the principle holds for both species. On a label the ratio is not printed directly; you can estimate it from the calcium and phosphorus percentages in the analytical constituents. The ratio also connects to the [protein-to-phosphorus ratio](/glossary/protein-to-phosphorus-ratio) discussion around kidney health. See the [Petipedia glossary](/glossary) for related entries.

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