How to Calculate Protein & Carbs in Cat Food

Controversy surrounds the inclusion of carbohydrates in cat food. Cats are obligate carnivores after all, and as such, their natural diet is quite low in carbohydrates. In this natural diet, they get some carbs from the intestinal tracts of the animals they eat, but that’s about it.

With more interest in feline nutrition and cat guardians seeking food choices that mimic a cat’s natural diet, there is a need to know how many carbohydrates a cat food contains.  Unfortunately, labeling regulations do not mandate that a carbohydrate percentage be listed, but you can figure it out yourself if you’re up to a bit of math.

Cat food labels must list the minimum crude protein percentage, minimum crude fat percentage, maximum crude fiber percentage, and maximum moisture percentage. They will also sometimes include a maximum value for ash. If this is not present, we use an estimate of 3% for canned foods and 6% for dry to make calculated estimates.

Step 1

Once you add up protein, fat, fiber, moisture, and ash, the only thing left is carbohydrate.

Here is a sample cat CAN food guaranteed analysis:

  • Crude Protein (min): 12%
  • Crude Fat (min): 2.0%
  • Crude Fiber (max): 1.5%
  • Moisture (max): 80%
  • Ash (max): 3%

Therefore, this food’s carbohydrate content is 100 – (12 + 2 + 1.5 + 80 + 3) = 1.5%

Now, these answers aren’t going to be exact because we are dealing with minimums and maximums and sometimes an estimate for ash, but it’ll get you into the ballpark.

In comparison, here is a sample cat DRY food guaranteed analysis:

  • Crude Protein (min): 38%
  • Crude Fat (min): 8.5%
  • Crude Fiber (max): 4.3%
  • Moisture (max): 12%
  • Ash (max): 6%

To calculate the carbohydrate content: 100 – (38 + 8.5 + 4.3 + 12 + 6) = 31.2%

WAIT, we are not done!

Step 2

Now both of these products report their guaranteed analyses on an “as fed” basis, meaning that comparing dry and canned foods is almost impossible due to their wildly different moisture contents. To correct for this we need to convert our result into a “dry matter” basis. Here’s how:

Find the percent moisture and subtract that number from 100. This is the percent dry matter for the food.

Step 3

Next divide the nutrient (Carbs or Protein) percentage on the label that you are interested in by the percent dry matter for the food and multiply by 100. The resulting number is the nutrient percentage on a dry matter basis.

For example, the dry food label lists its moisture content at 12% and we calculated percent of carbohydrate to be 31.2%. To figure out the food’s carb level on a dry matter basis, the calculations in this case would be 100-12=88 and then 31.2/88 x 100 = 35.4%. The canned food’s calculations look like 100-80 = 20 and 1.5/20 x 100 = 7.5%.

Now, you can appropriately COMPARE the carbohydrate “dry matter” percentage of the dry and can food. You will find in this example, and in most, that the dry food (35%) has a much higher carbohydrate content than can food (7.5%).

The Formulas Summarized

Step 1
100% minus – (Protein % + Fat % + Fiber % + Moisture % + Ash %)  =  Carbohydrate %  (not of dry matter)
Step 2
100% minus – Moisture % = Dry Matter %
Step 3
(Carb % divided / by Dry Matter %) multiplied x by 100 = Carbohydrate % of the Dry Matter

Now you know how to figure out how many Carbs (and Protein, just substitute Carb for Protein in formulas) are in your cat’s “dry matter” food. This way you can compare can and dry food or even one type of can food with another can food.

If you need help calculating, send an email to us. We are happy to help.

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