Calculating phorphorus?? Confused.

[TootsieT]

Hi again,

I am hoping someone can help me understand how to calculate phosphorus. Some pet food websites say things like:

Dry Matter %Phosphorus 1.35% When fed: 0.4.

I have no idea what this means. I did Google but so much is coming up and I am feeling so overwhelmed I am unable to process it all. I gave it a rest last night to start fresh today and still feel the same.

Even the Tanya chart (which is amazing someone did this for us all) confused me... See my example above: 1.35% phosphorus but then when fed it is only 0.4% and the chart says to give foods under .05%. So are we basing this on the when fed? Or the "Dry Matter" and what is dry matter?? Thank you for bearing with me on this. I want to understand so I know what to get my 15 year old lil lady who has been trying so many foods this year it cannot be helping her IBD.

 

[Maurey]

As fed is based off the percentage with water in. I.e, as you feed it. DMB is the percentage phos takes up of the food, disregarding the water.

 

[TootsieT]

As fed is based off the percentage with water in. I.e, as you feed it. DMB is the percentage phos takes up of the food, disregarding the water.

Thank you - so we should be using the as fed number and not the dry matter if I am understanding it right? So the food she is on right now at 1.35% dry and .4% as fed means she is under the Tanya chart recommendation of below .5%. If I am incorrect, seems finding food under .5% dry matter will be tough. Guessing as I type this it is the latter or there would not be a need for her chart of forums. Guess I talked myself through that one! LOL thank you for bearing with me as I "thought out loud" to you.

 

[FeebysOwner]

Dry matter basis is the most accurate number to use when dealing with phosphorus (along with most other nutritional values, actually). So, 1.35% is what you are dealing with and that is the basis that Tanya's charts are dealing with. As you said, Tanya's web site also says it is nearly impossible to get most foods that contain the goal of 0.5% phosphorus - which is the number on a dry matter basis.

Your goal is to get as close as possible and trust me it isn't easy especially if you have a picky cat. Use her chart as you can. Any foods that aren't on that chart, you will need to contact the company and ask for the phosphorus level on a dry matter basis, if you can't find it elsewhere. I have done that with a few companies, and so far, they seem to be very cooperative.

When Feeby's numbers get to the point that she might need a phosphorus binder - based on what I have read on Tanya's site - I will be pushing for one because Feeby won't eat most the foods that contain the lower amounts of phosphorus. Another thing to keep in mind for your cat.
Tanya's Comprehensive Guide to Feline Chronic Kidney Disease - The Importance of Phosphorus Control (felinecrf.org)

 

[TootsieT]

Dry matter basis is the most accurate number to use when dealing with phosphorus (along with most other nutritional values, actually). So, 1.35% is what you are dealing with and that is the basis that Tanya's charts are dealing with. As you said, Tanya's web site also says it is nearly impossible to get most foods that contain the goal of 0.5% phosphorus - which is the number on a dry matter basis.

Your goal is to get as close as possible and trust me it isn't easy especially if you have a picky cat. Use her chart as you can. Any foods that aren't on that chart, you will need to contact the company and ask for the phosphorus level on a dry matter basis, if you can't find it elsewhere. I have done that with a few companies, and so far, they seem to be very cooperative.

When Feeby's numbers get to the point that she might need a phosphorus binder - based on what I have read on Tanya's site - I will be pushing for one because Feeby won't eat most the foods that contain the lower amounts of phosphorus. Another thing to keep in mind for your cat.
Tanya's Comprehensive Guide to Feline Chronic Kidney Disease - The Importance of Phosphorus Control (felinecrf.org)

Thank you -- this is extremely helpful.