Phosphoric Acid

It is an undesirable additive for older cats and cats with kidney problems, and it shows up more often in low-cost foods.

Phosphoric acid is a mineral acid that FDA lists on its GRAS list for animal feed. In cat food it adds flavor and makes urine more acidic. It also supplies inorganic phosphorus, and a 2019 study in cats fed diets with added inorganic phosphorus found kidney changes at the higher levels tested. If your cat is older or has kidney disease, ask your veterinarian about the food.

Source: doi.org

Phosphoric acid is an acid made from phosphate rock. In cat food it is sprayed on or mixed in to add a tangy flavor that cats like and to lower urine pH. It also adds phosphorus. It appears on a large share of dry cat foods.

Yes, that is one reason it is used. The Merck Veterinary Manual explains that struvite crystals form more easily in neutral to alkaline urine, while calcium oxalate is favored in acidic urine. Merck also notes that struvite stones have become less common in cats, likely because of changes in commercial diets. Too much acidification is not the goal either.

Source: merckvetmanual.com

Researchers fed adult cats diets with added inorganic phosphorus. In one study, with about 3.6 g per 1000 kcal, kidney function fell within 4 weeks and the study was stopped. In a second study, with about 1.5 g per 1000 kcal, kidney function did not change significantly, but 36% of test cats showed kidney changes on ultrasound. The authors said dietary phosphorus may contribute to kidney changes.

Source: doi.org

Pettings gives phosphoric acid 2 out of 5 and lists it as a phosphate or acid additive. It appears on 50 of the 149 dry cat foods we list. The score weighs its use for urine acidity and taste against the quickly absorbed phosphorus it adds. Each food's page shows how it scores overall.