Updated: Mar 17, 2019
This study by Alexander et al. was published in December 2018 and raises some thought-provoking concerns about dietary phosphorus and healthy adult cats. For anyone with an interest in feline nutrition it's definitely worth a read.
As the authors mention, there is currently no safe upper limit for feline dietary phosphorus cited in nutritional guidelines set out by the US National Research Council (NRC), European Pet Food Industry Federation or Association of American Feed Control Officials (AAFCO). The authors of this study found that feeding a high phosphorus diet (4·8 g/1000 kcal total phosphorus, with a Ca:P of 0·6 and formulated to contain 5·2 % (3·6 g/ 1000 kcal) sodium dihydrogen phosphate, causes renal dysfunction in healthy adult cats.
In addition, their second study demonstrated that prolonged feeding of a diet with a total dietary phosphorus content of 3·6 g/1000 kcal, Ca:P 0·9, formulated to contain 2·2 % (1·5 g/1000 kcal) sodium dihydrogen phosphate results in no change in renal function in most cats. However, the authors highlight that sonographic changes to the kidneys were observed in some individuals, and although the clinical significance of these is not known, in a small number of cats renal dysfunction did occur.
Here's another interesting recent paper on this topic by Dobenecker at al. (2018):
In this study, the authors supplemented the diet of 23 cats with either calcium monophosphate (HP‐CaP) or sodium monophosphate (HP‐NaP) to create a high phosphorus diet. What they found was that supplementing the diet with sodium monophosphate led to a higher renal phosphorus excretion, when compared with calcium monophosphate.
They also observed that 7 out of 13 cats fed the sodium monophosphate-supplemented diet developed glucosuria, a potential indicator of renal damage. Their conclusion was that highly water‐soluble inorganic phosphorus sources such as sodium phosphate are likely to lead to phosphaturia, and may present a risk for renal health of cats.
So what are the implications of this? Well, there's definitely a need to determine a safe upper limit for both total and inorganic dietary phosphorus for cats.
Research on this important concern will certainly be ongoing, so hopefully we should have more information soon. Again, if you would like help or advice regarding your cat's diet, or if you have any questions, please email us: firstname.lastname@example.org