Changes in nutrition may be involved in the progressive increase in feline calcium oxalate (CaOx) urolithiasis, as oxalates are a product of the incomplete oxidation of dietary carbohydrate. This study examined whether a high carbohydrate diet would induce endogenous oxalate synthesis, causing increased urinary CaOx excretion and increasing risk for CaOx urolithiasis. A pilot study (n = 4 cats) established that when diet changed, CaOx excretion levels adapted and reached a steady state after 5.9 ± 0.7 days. For the experiment, 12 healthy adult female cats were first fed a high protein (HP) diet, then a high carbohydrate (HC) diet, followed by a high fat (HF) diet. Urine was collected on days 9–11 of each phase and analyzed for specific gravity, pH, urine oxalate (UOx) and urine creatinine (Ucreat) concentrations and total UOx excretion. UOx and Ucreat concentrations were significantly lower with HP compared with HC and HF. However, neither UOx excretion nor UOx:Ucreat ratio were significantly influenced by diet. Blood was collected on day 12, and plasma oxalate concentration was significantly lower when cats ate HP compared with HF. HC diets were not proved to induce endogenous oxalate synthesis in cats: possibly the metabolic pathway involved in oxalate synthesis did not reach threshold or the mechanism is more complex than proposed.

Commentary
This study attempted to discover why feline CaOx urolithiasis prevalence has recently increased. By offering 3 different diets, the researchers investigated differences in UOx excretion. HP was associated with slightly more acidic and concentrated urine, with no significant difference in UOx excretion. Several limitations were present; for instance, young adult, intact, lean, female cats were used, while CaOx stones are more common in older, overweight, neutered cats. The cats were fed experimental semipurified, wet diets rather than commercially available dry products. Further research is needed to define risk factors for CaOx urolithiasis.—Craig Datz, DVM, MS, DABVP, DACVN

Source
Changes in dietary macronutrient profile do not appear to affect endogenous urinary oxalate excretion in healthy adult cats. Dijcker JC, Hagen-Plantinga EA, Hendriks WH. VET J 194:235-239, 2012.