Why some phosphates added in cat food are bad for cats

Jojo&Tutu

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I spoke to my veterinarian nutritionist Dr. Lisa Weeth DVM DACVN of Metropolitan Animal Specialty Hospital, Los Angeles, California. I will try to relay her advice. She initially advised me to stay away from cat foods that have Dicalcium or Tricalcium phosphates in them. I did some research and found a problem with Sodium tripolyphosphates.
I asked her why tricalcium phosphate or dicalcium phosphates are bad for a cat and also about sodium tripolyphosphate. She said:

If calcium phosphate is from bone meal it’s ok but if it is not from meat or bone it can grab onto other minerals so minerals end up depositing in the kidneys which is damaging to the kidneys. A lot depends on how much of the phosphorus in the formula is from tricalcium-phosphate or dicalcium-phosphate. The pet food manufacturers uses these as a cheap available source for calcium. If low on the list of ingredients it is likely ok. If more of the phosphorus in the diet is coming from it then it is a problem for the kidneys - increase markers of kidney damage were found in the cats in research. Purina and Royal Canin sponsored the research. They should be adjusting their cat diets.

Regarding Sodium tripolyphosphate;
This Is often used to prevent tarter. Sodium breaks apart calcium phosphorus complex forms and binds to calcium preventing plaque forming. However in the gastro-intestinal system it causes phosphorus to enter blood more rapidly at higher available levels which is like having more phosphorus in the formula which can affect the kidneys. Calcium dampers the effect. Dr. Weeth said the calcium phosphorus ratio should be not less than 1:1 and not more that 2:1 (greater calcium).
Here’s the research summary on the sodium tripolyphosphate that I found:

https://onlinelibrary.wiley.com/doi/full/10.1111/jvim.15961

I hope this clarifies my previous posts.
 
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Furballsmom

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Thanks very much for sharing this information, I found it very helpful. For Mr Captain, I was particluarly interested in the part about sodium tripolyphosphate.
 
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Jojo&Tutu

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Thanks very much for sharing this information, I found it very helpful. For Mr Captain, I was particluarly interested in the part about sodium tripolyphosphate.
I wish Royal Canin would remove it from their PR rabbit limited ingredient formula altogether. I chose Hills Dental treats over Royal Canin because it doesn’t have it in it.
 
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Jojo&Tutu

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I woke up this morning and thought of something else my nutrition veterinarian said that I should clarify. It has to do with the percentage of phosphorus that is from tricalcium phosphate or dicalcium phosphate vs natural sources like ground up bone. If it only 30% from tricalcium or dicalcium phosphate that’s ok but if it is like 70% that’s when it is a problem. That’s when she said if it is low on the list of ingredients there is likely another source of phosphorus (hopefully). Wish the food manufacturers will list clarifications on that. Maybe we should start requesting that information so they list it somewhere on their website. ask What is the percentage of phosphorus in the formula that is from tricalcium phosphate or dicalcium phosphate? That a bit of a different question than what is the percentage of phosphorus (on a dry matter basis) that is in the whole formula.?
 
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