Cat eating


Importance of phosphorous levels in cats' diets

Science is about constantly expanding our knowledge and understanding. At Waltham, our research is focused on uncovering how we can help improve the lives and health of pets. Although, perhaps not the most exciting topic to some, the key nutrients in our diets are critical for health. This is even more true for pets who are fed complete and balanced meals. This means that all the nutrients they are every day provided are at the correct levels – not too much, but not too little.

Phosphorus is one of these key nutrients. Perhaps more familiar to those who have studied biology for its close relationship with calcium- the calcium/phosphorus ratio. Disruption from an ideal ratio of 1-2:1 can cause bone and development problems in animals. However, some findings from Munich University raised some questions about the levels of phosphorus in feline diets. And so our curiosity to understand more about what may be going on led to our research studies and our published findings.

Jumping straight to the punch line- we found that recommended upper level of phosphorus in cat food needed to be reduced as it may contribute to chronic kidney disease. Our results demonstrated a new safe level of phosphorus in feline diets (1g/1000kcal of inorganic phosphorus (P) and either 4.0g/1000kcal of total dietary P in combination with a Ca: P ratio of 1.0,  or 5.0 g/1000kcal of total dietary P in combination with a Ca: P ratio of 1.3).

It sounds simple when you can give a conclusion in a sentence. But the reality is a little different. To be confident in this recommendation, multiple studies were done to delve into the results. That means several scientists (nutritionists, veterinarians, biologists, chemists, statisticians & data scientists), cats, and their trainers were involved as well.

Throughout this journey to understand the complex relationship of phosphorus, calcium, cats and kidneys, we have shared our findings with others through peer-reviewed publications, conference presentations, and blogs to ensure that this critical knowledge reaches those who need it. We want everyone to support us in our purpose: A BETTER WORLD FOR PETS.

Further reading:

Alexander et al. 2019. Effects of the long-term feeding of diets enriched with inorganic phosphorus on the adult feline kidney and phosphorus metabolism. British Journal of Nutrition. 121(3), 249-269. 

Coltherd et al. 2019. Not all forms of dietary phosphorus are equal: an evaluation of postprandial phosphorus concentrations in the plasma of the cat. British Journal of Nutrition, 121(3), 270-284. 

LaFlamme et al. 2020. A review of phosphorus homeostasis and the impact of different types and amounts of dietary phosphate on metabolism and renal health in cats. Journal of Veterinary Internal Medicine. 34: 2187-2196.

Soutar et al. 2021. Comparisons of In Vitro and In Vivo Digestibility Assays for Phosphorus in Feline Diets and Associations with Dietary Nutrient Content. J Agric. Food Chem, 69(36), 10688-10699.

Coltherd et al. 2021. Towards establishing no observed adverse effect levels (NOAEL) for different sources of dietary phosphorus in feline adult diets: Results from a 7-month feeding study. British Journal of Nutrition, 126(11), 1626-1641.

Coltherd et al. 2021. Dietary calcium to phosphorus ratio affects postprandial phosphorus concentrations in feline plasma. British Journal of Nutrition. Preprint.


Dietary phosphorus: how much is too much for cats?
Working in partnership: the interaction of dietary calcium and phosphorus.


ECVIM Oral presentation
ESVCN 2020