Abstract-only review · 2019
High inorganic phosphorus diets and feline kidney measurements
Adverse kidney findings depended on the tested phosphorus formulation and calcium balance.
Review scope
This summary is based on the published abstract. We have not appraised the full methods, tables or supplementary material. Details absent from the abstract remain unverified.
Question and design
Two studies involving 48 and 50 healthy adult cats. Diets with higher total and inorganic phosphorus and lower calcium:phosphorus ratios. Comparator: Lower-phosphorus control foods.
What was measured?
Kidney filtration, ultrasound, health markers and mineral balance.
Main findings
The first study stopped after four weeks because of adverse kidney findings. In the second, mean filtration did not change, but ultrasound changes occurred in 36% of test cats; stones in both groups complicated interpretation.
Study strengths
Controlled feeding with functional and structural kidney measurements.
Limitations
Phosphorus amount, source and calcium ratio changed together. A universal safe limit cannot be isolated from these comparisons.
Researchers’ conclusion
The authors called for further investigation of phosphorus sources and calcium balance.
Ingredients investigated
Multi-ingredient formulations
Phosphorus
Multi ingredient · cat. Two studies involving 48 and 50 healthy adult cats.
Tested form: Diets with higher total and inorganic phosphorus and lower calcium:phosphorus ratios; exact salt source and amounts not reported in the reviewed abstract. Dose: Higher total/inorganic phosphorus; numeric amount not reported in the reviewed abstract (Dietary inclusion and calcium:phosphorus ratio). Duration: The first study stopped after four weeks; duration of the second study not reported in the abstract. Comparator: Lower-phosphorus control foods.
Measured finding: The first study stopped after four weeks because of adverse kidney findings. In the second, mean filtration did not change, but ultrasound changes occurred in 36% of test cats; stones in both groups complicated interpretation.
Limitations: Phosphorus amount, source, and calcium ratio changed together. A universal safe limit cannot be isolated from these comparisons.
This ingredient was part of a combined formulation; the study does not isolate its contribution.
Calcium
Multi ingredient · cat. Two studies involving 48 and 50 healthy adult cats.
Tested form: Diets with higher total/inorganic phosphorus and lower calcium:phosphorus ratios; exact calcium source and amount not reported in the reviewed abstract. Dose: Lower calcium:phosphorus ratio; exact calcium amount not reported in the abstract (Dietary mineral ratio). Duration: The first study stopped after four weeks; duration of the second study not reported in the abstract. Comparator: Lower-phosphorus control foods.
Measured finding: The first study stopped after four weeks because of adverse kidney findings. In the second, mean filtration did not change, but ultrasound changes occurred in 36% of test cats; stones in both groups complicated interpretation.
Limitations: Phosphorus amount, source, and calcium ratio changed together. A universal safe limit cannot be isolated from these comparisons.
This ingredient was part of a combined formulation; the study does not isolate its contribution.
Evidence.pet interpretation
The study warrants formulation-specific scrutiny. An ingredient list alone cannot reveal the exposure tested here.
Funding and conflicts
The source identifies Mars Petcare funding. Full conflict declarations and methods were not appraised for this abstract-based summary.
Source and review date
Alexander J et al. Effects of the long-term feeding of diets enriched with inorganic phosphorus on the adult feline kidney and phosphorus metabolism. British Journal of Nutrition. 2019. PMCID: PMC6390406.
STU-041. Reviewed 25 September 2026. Next review 25 December 2026.