Jonathan Stockman, Department of Veterinary Clinical Services, College of Veterinary Medicine, Long Island University, New York, USA put together some research discussing the current state (2024) of dietary phosphorus and renal disease in cats and what we know.
Phosphorus is a nutrient that is required by every cell in the cat’s body to function normally. Too low of phosphorus can cause negative effects. Too high of phosphorus can lead to a further decrease in kidney function.
There is no upper safety limit for how much phosphorus can be in cat food set by any organizations. And phosphorus in different diets can absorb differently. So that makes it hard to say whether certain diets are actually safe long-term. IRIS gives targets for blood phosphorus in different stages of CKD, but information is limited on how much phosphorus cats with CKD should actually be having.
Phosphorus is a mineral every cat needs. It’s found in every cell of the body, and mostly stored in bones. Kittens need the most phosphorus because their bones are growing quickly, but adult cats still need a steady supply. Hormones and calcium help regulate all this. The intestines absorb phosphorus from food, and the kidneys control how much phosphorus stays in the body. Kidneys can either reabsorb the phosphorus (keep it) or let it go out in the urine.
As kidney function declines, the kidneys can’t filter phosphorus out of the blood as well. This can cause build ups and overaccumulation of phosphorus. When phosphorus goes up or calcium goes down, the body releases a hormone that tries to correct this by pulling calcium out of the bones that can cause weakening and other negative effects.
High phosphorus intake might even be linked to increasing the odds of kidney disease developing in otherwise healthy cats. Obviously our CKD cats generally are older and should especially consider this for our group. There are other studies done where they fed different phosphorus levels, and have linked higher phosphorus diets to a decrease in GFR, increase in creatinine levels, and other conditions worsening related to kidneys. The same for low phosphorus but opposite results, showing fewer negative renal changes. The data is more limited for cats in early stage renal disease, the benefits of reduced phosphorus over potentially losing weight and muscle mass are unclear.
Watch the appetite, if caloric intake of these lower phosphorus foods is low, cats might suffer from loss of body mass and muscle which is counterproductive.
The International Renal Interest Society (IRIS) suggests trying to keep phosphorus <4.6 mg/dL (<1.5 mmol/L) in Stage 1 and 2 cats, <5.0 mg/dL (<1.6 mmol/L) in Stage 3 cats, and <6.0 mg/dL (<1.9 mmol/L) in Stage 4 cats.
We have some ways we can do that. IRIS recommends a renal therapeutic diet in Stage 2 cats. But consider the other concerns of restricting protein at this stage. Also note that these specific guidelines are for dogs AND cats. Another option is a traditional diet with phosphorus binders. There are a lot of binder options available. Discuss your lab values and specific situation with your vet to come up with the best path forward to increase longevity.
So, in conclusion, and offering my personal take - phosphorus is important for overall function of our cat’s bodies. Too little is bad, too much is bad. But knowing what those exact value constraints are is a challenge right now. For early stage CKD cats, if you have the option to feed two different foods, similar ingredients but one has a little lower phosphorus than the other, it seems like a wise decision to feed the lower phosphorus and continue to monitor. Later stage CKD the urgency to reduce phosphorus might be greater. The correlation between high phosphorus levels and increased kidney damage seems pretty strong. Individual cats process phosphorus differently so there isn’t a one-size-fits-all statement for managing phosphorus.
Sources:
Dietary phosphorus and renal disease in cats: where are we? - PMC
https://www.idexx.com/files/iris-pocket-guide-2.pdf
The role of phosphorus in feline chronic renal disease (Proceedings) | dvm360
Phosphorus is a nutrient that is required by every cell in the cat’s body to function normally. Too low of phosphorus can cause negative effects. Too high of phosphorus can lead to a further decrease in kidney function.
There is no upper safety limit for how much phosphorus can be in cat food set by any organizations. And phosphorus in different diets can absorb differently. So that makes it hard to say whether certain diets are actually safe long-term. IRIS gives targets for blood phosphorus in different stages of CKD, but information is limited on how much phosphorus cats with CKD should actually be having.
Phosphorus is a mineral every cat needs. It’s found in every cell of the body, and mostly stored in bones. Kittens need the most phosphorus because their bones are growing quickly, but adult cats still need a steady supply. Hormones and calcium help regulate all this. The intestines absorb phosphorus from food, and the kidneys control how much phosphorus stays in the body. Kidneys can either reabsorb the phosphorus (keep it) or let it go out in the urine.
As kidney function declines, the kidneys can’t filter phosphorus out of the blood as well. This can cause build ups and overaccumulation of phosphorus. When phosphorus goes up or calcium goes down, the body releases a hormone that tries to correct this by pulling calcium out of the bones that can cause weakening and other negative effects.
High phosphorus intake might even be linked to increasing the odds of kidney disease developing in otherwise healthy cats. Obviously our CKD cats generally are older and should especially consider this for our group. There are other studies done where they fed different phosphorus levels, and have linked higher phosphorus diets to a decrease in GFR, increase in creatinine levels, and other conditions worsening related to kidneys. The same for low phosphorus but opposite results, showing fewer negative renal changes. The data is more limited for cats in early stage renal disease, the benefits of reduced phosphorus over potentially losing weight and muscle mass are unclear.
Watch the appetite, if caloric intake of these lower phosphorus foods is low, cats might suffer from loss of body mass and muscle which is counterproductive.
The International Renal Interest Society (IRIS) suggests trying to keep phosphorus <4.6 mg/dL (<1.5 mmol/L) in Stage 1 and 2 cats, <5.0 mg/dL (<1.6 mmol/L) in Stage 3 cats, and <6.0 mg/dL (<1.9 mmol/L) in Stage 4 cats.
We have some ways we can do that. IRIS recommends a renal therapeutic diet in Stage 2 cats. But consider the other concerns of restricting protein at this stage. Also note that these specific guidelines are for dogs AND cats. Another option is a traditional diet with phosphorus binders. There are a lot of binder options available. Discuss your lab values and specific situation with your vet to come up with the best path forward to increase longevity.
So, in conclusion, and offering my personal take - phosphorus is important for overall function of our cat’s bodies. Too little is bad, too much is bad. But knowing what those exact value constraints are is a challenge right now. For early stage CKD cats, if you have the option to feed two different foods, similar ingredients but one has a little lower phosphorus than the other, it seems like a wise decision to feed the lower phosphorus and continue to monitor. Later stage CKD the urgency to reduce phosphorus might be greater. The correlation between high phosphorus levels and increased kidney damage seems pretty strong. Individual cats process phosphorus differently so there isn’t a one-size-fits-all statement for managing phosphorus.
Sources:
Dietary phosphorus and renal disease in cats: where are we? - PMC
https://www.idexx.com/files/iris-pocket-guide-2.pdf
The role of phosphorus in feline chronic renal disease (Proceedings) | dvm360