“The solution to pollution is dilution” is the phrase we veterinarians now use to explain how to prevent urinary crystal and stone formation. Time, observation, and studies have shown us that there are no magical diets for solving this problem and that water consumption is key.


Different types of crystals and stones form depending on whether the urine is acidic or alkaline. Special diets limit certain minerals and manipulate the ingredients to create a urine pH (measurement of acidity or alkalinity) that is unfavorable for crystals and stones to form. Those of you with pets that have had multiple surgeries to remove bladder stones are well aware of the limitations of these diets to successfully prevent stone formation. The answer appears to be water, H2O, and more water.


The more dilute urine is the less likely minerals can clump together to form crystals and stones, no matter what the urine pH. This knowledge is extremely important for cat owners but is also a major problem for them. Why?


Cats are extremely thirst tolerant. They are also capable of conserving body water by concentrating their urine much greater than dogs or humans. These evolutionary adaptations make sense for a carnivore that evolved in a dry, desert climate. Cats obtain most of their water from their prey. Rodents, birds, and small reptiles are 60% water!


What this means is that cats are much less likely to seek sources of water even when their body needs it. This is the main reason they are so susceptible to urinary crystals and stones. The more concentrated the urine the more likely minerals can become crystals and eventually stones. This has been the major reason that special dry diets have such variable results with preventing urinary crystals and stones in cats. These diets only contain 10% water.


So how do you make a cat drink more water? You can’t. But you can get more water into them by changing their diet.


I have spent my entire veterinary career trying to convince cat owners that a wet food diet was more important than the brand of diet for cats with a tendency to form urinary crystals. More water and dilute urine are for more important than the urine pH and ash content of the diet. In fact, we now know that the ash content of the diets is largely an irrelevant concern.


Preliminary results from recent research by veterinary teams in France and Germany demonstrate this. The scientists compared the urine of cats fed a wet food, a homemade poultry and rice with zucchini diet, a dry food with zucchini, and a dry food without zucchini. It is not clear if zucchini was added to the diets to increase the water content, the fiber content, or both. 


The findings suggested that wet and homemade diets were more effective for preventing calcium oxalate crystal formation. Calcium oxalate is presently the most common crystal and stone found in cats. Their findings were mixed with regards to struvite crystal prevention.


Experience with my homemade diets in dogs has shown great success for those suffering from struvite and oxalate crystal formation. In fact, it is possible to formulate a homemade recipe that is virtually oxalate free.


Without any recipe manipulations, we have been successful in dissolving kidney and bladder struvite stones and preventing the recurrence of both struvite and oxalate crystals. I attribute the success primarily to the water content of the homemade diets for struvites and the combination of water and ingredient selection for oxalates.


The take home for those of you with cats and dogs that are urine crystal formers is to increase the amount of water in the diet.


That can be achieved easily by adding water to their dry and wet foods. Dog owners may want to consult with their vets about the amount of salt to add to the diet to drive thirst and additional water consumption. Use salt with caution in cats due to their natural thirst tolerance. Your vet may have other suggestions for increasing daily water consumption for your cat.


Dr. Ken Tudor