Reduction of struvite and calcium oxalate in cat urine through the diet?

Customers having this problem with their cats keep come to me for many reasons. I would say the most cited one is that their cat has been diagnosed by their vet and prescribed a specific, though helpful, yet very expensive diet. This brings up the question of which dietary factors have to be considered and what are the non prescription options if there are any.
I have looked a little deeper into the issue. To say that the problem is strictly due to wrong feeding is only partially, if, in some cases, at all true. Additionally this opinion is strongly supported by vets who keep prescribing specific diets to cure the condition. It appears as if there is no evidence that a diet directly causes feline lower urinary tract disease, also short called FLUTD. However it also looks like that there is definitely some evidence that a diet may increase the risk that a cat may develop urinary crystals, stones or (urethal) plugs.
Let’s start with what we know for sure: Development of crystals and stones is by large depending on urine pH, urine volume, and mineral concentration in the urine, feeding habits/schedule (i.e. scheduled or free choice all day) and/or genetics.
A veterinarian study performed by the pet food industry addressing the issue reveals: Crystals and stones containing struvite (= magnesium ammonium phosphate) were common in cats (more so than in dogs). Because of this the pet food industry developed diets designed to minimize the risk of struvite forming. These diets were low in magnesium and caused the cats eating them to produce acidic urine with a low pH value. When cats were fed these specific diets, the percentage of those with struvite stones decreased from 75% in 84 to 48% in 1995. However, at the same time the number of cases with calcium oxalate crystals and stones went up from 2% in 84 to 40% in 1995. As of today, struvite is still the more common component of urethal plugs.
Dietary factors affecting struvite crystals development appear to be concentration of magnesium, urine ph and water consumption. The dietary factors affecting struvite stones (or uroliths) minimizing the risk are low to moderate protein content and low magnesium values. Additionally it is also a fact that besides decreasing the magnesium content of a diet, acidifying the urine is even more helpful.
This means the diet you feed your cat can indeed influence the health of the urinary tract. Controlling mineral levels, changing the urine pH, increasing water intake and adjusting feeding schedules reduces the risk of a cat developing urinary crystals and stones. Following are diet related issues to keep in mind when feeding a cat suffering from the condition.
The FDA does allow statements such as for example “reduces urine pH to help maintain urinary tract health”, however at the same time requires that such statements only are made if the food delivers on the promise. Such determinations are made based on controlled veterinary studies, which provide data used to ensure this safety. Pet food manufactures walk a fine line here because too much acidifying can cause serious health problems for the animal. The feeding directions need to say that the diet is for adult maintenance only (since safety for kittens and pregnant cats has not been established yet) and that the food is to be used as a stand alone diet to be fed throughout the day. While talking about feeding another factor plays an important role: Water. Water supply and consumption is an important part as it influences the development of urinary crystals and stones. Provide ample water supply. This results in a lower urine concentration and thereby reduces the risk of stone or crystal formation. More water means more urine. More urine translates into shorter urine presence in the bladder. Cats naturally are not crazy about drinking water due to the fact that they simply do not need as much water as other animals. You may have to play a more enforcing role. Try providing numerous bowls in various easy accessible locations, running water, flavor enhanced water and mixing water into the food.
Another important factor is the mineral concentration in the food. This includes magnesium and phosphorus. Look for the ash content on the label. Ash is considered the inorganic portion of a food remaining in the food after it is burned at 600 degrees Celsius for a 2 hour period. Ash includes calcium, magnesium, phosphorus, sodium, potassium, manganese and trace minerals. AAFCO in its nutrient diet profiles for cats requires minimum values of these components to be present in cat food. FDA requirements state that a “low ash” claim is not allowed on cat food. Such or similar claims, even if they don’t reference FLUTD, are inherently false and misleading and originally were based on a by now outdated scientific consensus, which concluded that ash is not related FLUTD. Basically, there are no valid reasons to reference ash on the product label (other than in the guaranteed analysis) except in regard to this outdated theory.
In the past it was generally assumed that lowering dietary magnesium would be important to lowering the risk of struvite formation. Magnesium is one of the constituents of ash. This led people to assume that a low ash content in food meant it was low in magnesium. That is simply wrong. Low ash diets could contain normal amounts of magnesium, but be lower in any of the other minerals. According to FDA guidelines, in order for a food to be considered “low magnesium” it must be present with less than 0.12% (dry matter basis) and less than 25 mg/100 Kcal.
With regards to magnesium, further consideration has to be given to its actual form as it is present in a food. Back in the seventies research demonstrated that high levels of magnesium oxide in a food could contribute to the formation of stones. More current research shows that this is simply not true if the magnesium is in the form of magnesium chloride. It appears as if magnesium oxide causes alkaline urine while magnesium chloride results in the formation of acidic urine.
Since phosphorus is a component of struvite, it should theoretically be of value to reduce dietary phosphorus in an attempt to reduce the formation of struvite stones and crystals. Slightly lower levels of dietary phosphorus may be beneficial, but extreme care needs to be taken to not reduce the phosphorus too much, since the ration of calcium to phosphorus is important to many body functions. Acidified diets have been proven to decrease phosphorus levels in adult cats. This could cause a calcium phosphorus imbalance.
Provide smaller amounts of food to cats at risk for developing struvite crystals or stones all day long rather than only feeding a larger meal once or twice a day. After eating a large meal, the pH of the urine usually becomes more alkaline. If the cat is fed smaller portions several times and throughout the day urine pH will stay more acidic. However, do not over feed. Keep in mind that over feeding results in more than the recommended amount of magnesium being consumed. The excessive amount of magnesium is excreted in the urine and may increase the risk of stone formation.
Some cats are genetically predisposed to develop oxalate crystals if they are fed diets resulting in acidic urine and low in magnesium. To reduce this risk, I usually recommend a diet formulated to contain moderate calcium, phosphorus, and magnesium levels and with decreased urine acidifying potential.
Calcium oxalate crystals and stones are more likely to occur in acidic urine. Excess levels of vitamin C in the diet can acidify urine and increase the risk of calcium oxalate crystals. Stay away from food with high vitamin C content.
Important: When feeding such a diet do not provide additional supplements with the specific goal to help this particular health condition. Neither magnesium, calcium nor phosphorus should be restricted or supplemented for the following reasons:
Diets that are either very high or very low in magnesium can increase the risk of calcium oxalate stones.
High levels of urinary calcium increase the risk of calcium oxalate crystals, especially in concentrated acidic urine. High urinary calcium results from excess intake of calcium in the diet, abnormal hormonal regulation of calcium levels by the parathyroid gland or hyperparathyroidism and excess vitamin D intake. At the same time it is important that calcium intake is not restricted too much. Decreasing calcium too much may increase the amount of calcium oxalate found in the urine. When calcium is high in the diet, it decreases the absorption of oxalate from the digestive system, and the excess oxalate is excreted in the feces. When dietary calcium is low, more of the oxalate is absorbed from the digestive system and is then excreted in the urine. Levels of phosphorus in the bloodstream affect the levels of calcium.
Vitamin D should be fed at a moderate level, since deficiencies or excesses of this vitamin can result in abnormal blood and urine calcium and phosphorus levels.
If all of this is of concern to you and you want specific suggestions with regards to which diets I recommend, please e-mail me.