The Truth About Grain-Free Cat Foods

Jennifer Coates, DVM
Aug 21, 2015
   |   3 min read
Image: Photo Grapher / via Image Bank

Do you feed a grain-free diet to your cat? Why?

The most common reason I hear goes something like this:

Cats are carnivores and their natural/ancestral diet contains almost no grain, so cat foods should not contain grain.

There’s nothing wrong with that line of reasoning… but as always, the devil is in the details.

Many people who buy grain-cat food actually think they are purchasing a carbohydrate-free product. Just substitute the word “carbohydrate” for “grain” in the statement above:

Cats are carnivores and their natural/ancestral diet contains almost no carbohydrates, so cat foods should not contain carbohydrates.

I’m right, yes?

But “grain-free” does not mean “carbohydrate-free.” Starch, a type of carbohydrate, is essential to the formation of cat food kibble. Without starch, the kibble will not hold together. Dry foods have to contain a significant amount of carbohydrate. The manufacturers of the grain-free products simply switch out the grains for non-grain carbohydrate sources. Take a look at the ingredient list. I guarantee you will see potato, sweet potato, tapioca, or other non-grain carbohydrates.

Why don’t we change our statement once again:

Cats are carnivores and their natural/ancestral diet contains almost no potato/sweet potato/tapioca, so cat foods should not contain potato/sweet potato/tapioca.

Still true, right?

If you truly want to avoid carbohydrates (grain and non-grain), you’ll have to feed a canned cat food. Check out the differences in carbohydrate levels between a typical dry and canned formulation. Sorry, it does take some math.

Add up the percentages for crude protein, crude fat, crude fiber, moisture, and ash, and subtract the result from 100%. The result is a ballpark figure for the food’s carbohydrate percentage. If a number for ash is not provided, use 6% as an estimate for dry food and 3% for canned.

Many manufacturers provide these numbers on an “as fed” rather than “dry matter” basis. If this is the case, you’ll need to convert your carbohydrate percentage to dry matter:

  1. Find the percent of moisture and subtract that number from 100. This is the percent dry matter for the food.
  1. Divide your carbohydrate percentage by the percent of dry matter and multiply by 100. The resulting number is the food’s carbohydrate percentage on a dry matter basis.

When I did these calculations for a dry and canned cat food that I had on hand, I came up with a carbohydrate percentage of 35.4% for the dry and 7.5% for the canned.

All canned cat foods are not created equal, either. When you do the math, you’ll find some that have a carbohydrate percentage in the single digits while others are almost as high as a dry food. For example, I looked at two canned cat foods made by the same manufacturer—one was 21.8% carbohydrate on a dry matter basis while the other was 9%.

Under 10% on a dry matter basis is a good, working definition of a low carbohydrate cat food. Unfortunately, you’ll have to do break out the calculator to see if your cat’s food fits the bill.

Dr. Jennifer Coates

Image: Master-L / Shutterstock

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