Dietary phosphorus and renal disease in cats: where are we?

Abstract

Practical relevance: Phosphorus is an essential nutrient required for the normal function of every cell in the body and a deficiency in dietary phosphorus may lead to adverse effects. Conversely, high dietary phosphorus may cause kidney damage in otherwise healthy adult cats, particularly when provided in highly bioavailable forms and when the calcium-to-phosphorus ratio is low. For cats that have chronic kidney disease (CKD), phosphorus is the most important mineral in its pathogenesis and morbidity. As the disease progresses, elevated phosphorus may increase the risk of complications such as soft tissue mineralization, which can lead to a further decrease in renal function. Additionally, the hormones secreted in response to increased circulating phosphorus have harmful effects, such as bone resorption, and can cause cardiovascular pathology. Very low phosphorus diets can also be problematic in cats with early CKD, potentially leading to hypercalcemia.

Clinical challenges: There is currently a lack of maximum safety limits for dietary phosphorus in accepted nutritional guidelines in North American and Europe, which makes it difficult to assess the safety of some higher phosphorus cat foods. Additionally, information regarding phosphorus bioavailability is unknown for many diets and there are no commercially available tests. Similarly, there is no consensus regarding phosphorus requirement and recommended intake in cats with International Renal Interest Society stage 1-4 CKD despite there being targets for serum phosphorus.

Aims: This review evaluates dietary phosphorus in healthy cats and cats with renal disease, and describes how newer research is informing evolving clinical approaches in feline nutrition.

Audience: The article is aimed at general practitioners, internal medicine specialists and veterinary nutritionists.

Evidence base: Information provided in this article is drawn from the published literature.

Keywords: Phosphorus; calcium; diet; fibroblast growth factor-23; kidney; parathyroid hormone; renal.

Figure 1

Adult cat suffering from chronic kidney disease and sarcopenia receiving supportive care in a veterinary clinic. Courtesy of Sam Taylor

Figure 2

Adult cat suffering from chronic kidney disease with an esophageal feeding tube. Courtesy of Sam Taylor