Confused about calculating carbs

[TraceyM]

Hello Everyone, my Mom's cat was diagnosed with Diabetes and we switched him over to a canned food diet. I have been using the calculations I found online to find food that is lower than 10% in Carbs but I recently found the very large long list posted by Dr Lisa Pierson and the one from Binky's page and some of the calculations of Carbs are much lower than what I come up with. For instance, I have not found a Friskies wet food that is under 10% in carbs but according to Dr Pierson's list, there are a lot. I'm so confused. HELP! I also am the director of an animal rescue in Ohio and this info would be very helpful to give to others. Our vet knew nothing of these calculations when I told her about this.

I was told you add up the protein, fat, fiber, moisture, and ash. Subtract that number from 100. Take the answer (say it's 4 and divide the from the difference of the moisture subtracted from 100. So if the moisture is 78 I would take 4 divided by .22 which gives me 18.18) That would be too high in carbs. But then I look at the charts and the carbs they have listed for the same food is under 10. I hope I'm making sense. I just want to know the right way to figure this out.

Thank you!!

 

[Larry and Kitties]

Sounds like you are calculating the % carbs from the guaranteed analysis listed on the cans. The guaranteed analysis is minimums and maximums and thus the calculated values are not really accurate for carbs For example the guaranteed analysis list a minimum of protein. If protein is actually higher than % carbs will be lower. Same for fat minimum.
Dr Pierson's list is based on the typical value for the constituents as measured in actual processed canned food.

 

[TraceyM]

Sounds like you are calculating the % carbs from the guaranteed analysis listed on the cans. The guaranteed analysis is minimums and maximums and thus the calculated values are not really accurate for carbs For example the guaranteed analysis list a minimum of protein. If protein is actually higher than % carbs will be lower. Same for fat minimum.
Dr Pierson's list is based on the typical value for the constituents as measured in actual processed canned food.

Thank you. The good news is on her chart, there's a lot more foods I can feed Sunny than what I had figured!

 

[Elizabeth and Bertie]

I was told you add up the protein, fat, fiber, moisture, and ash. Subtract that number from 100. Take the answer (say it's 4 and divide the from the difference of the moisture subtracted from 100. So if the moisture is 78 I would take 4 divided by .22 which gives me 18.18) That would be too high in carbs. But then I look at the charts and the carbs they have listed for the same food is under 10. I hope I'm making sense. I just want to know the right way to figure this out.

There's different ways of calculating carb values. What I think you've done in your example above is to first calculate the 'as fed' (wet matter) carb percentage by weight, and then deduct the moisture content to give you dry matter carb % by weight.

But some consider it more useful to take the calculation a stage further and calculate the 'percentage of calories' that come from carbohydrates. (That's because diabetics have been found to do best on foods that have less than 10% calories from carbs).
To do this (using either wet or dry matter values) you multiply protein and carbs %'s by 3.5, and the fat by 8.5 to get calories of each of those per 100g of food. Adding those up gives you the total calories per 100g of food.
Then you divide the calories from carbs per 100g by the total calories per 100g, and multiply by 100. That should give you the percentage of calories from carbs. This should give you the same values as found on Dr Lisa Pierson's list.

However... The data on US food labels may or may not be an accurate representation of what's in the can at any given time, because it states only minimum or maximum values for the various elements. Because of this it's necessary to contact the manufacturer for the current values. Dr Lisa Pierson has done this for all the foods in her list (Hurrah! )

...Incidentally, should you want it, I do have an ancient Excel spreadsheet that does the calculations really easily. If you'd like it just PM me your email address. It has my calculations on it but you can easily write over them.

Eliz