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Nutrition Nuggets is the newest offshoot of petMD's Cat Nutrition Center. Each week Dr. Coates will use her expertise and wisdom to blog about the intricacies of cat nutrition.

The Truth About Grain-Free Cat Foods

August 21, 2015 / (8) comments

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


Comments  8

Leave Comment
  • Substitutions
    08/21/2015 10:46pm

    Sounds a whole lot like when food items are labeled fat-free. Or sugar-free. It's my understanding that when things are "fat-free" the sugar is increased to enhance the flavor. The opposite is true for sugar-free. The fat content is increased to enhance the flavor

    Plus, what cat doesn't eat grass when they get a chance?

  • Not all kibble is created
    09/04/2015 05:06pm

    equal. Check out Orijen and Acana cat foods, made in Canada and high in protein, low in carbs. Championpetfoods.ca. My cats love it. It is pricey, but well worth it in my opinion.

  • Dry Cat Food
    09/04/2015 08:49pm

    "Would adding water; chicken; tuna or clam broth to dry Cat feed okay: or would that deplete the Fiber and Pre-biotic found in some dry feeds? Anne!

  • 09/05/2015 08:16pm

    Adding a significant amount of liquid will dilute out a variety of nutrients. Chances are the cat will just eat more volume to compensate, but it's hard to know for sure.

  • 09/05/2015 08:17pm

    Thanx Dr. Debra: "I wish a company would develop a Cat moist Pellet which is almost 90% Protein; (Turkey fish etc.); how do you feel about feeding my Kitty Tuna Fish as protein?

  • 09/05/2015 08:57pm

    Tuna is okay as an occasional treat or as a protein source within an balanced recipe for cat food... but NOT as a sole source of food for cats.

  • 09/05/2015 09:09pm

    HI Dr. Jennifer: (I apologize for my misnomer); I have been doing a lot of reading (articles; Cat Book etc.); very interesting about the origins of the Cat + basic diet. I simply cannot find the perfect food for my "Orange Tabby Queen"!: )

  • 09/06/2015 12:23am

    ps She eats only "Tuna; canned or pouch; Salmon; canned or pouch; and Swanson's canned Chicken;+Natural Pellets: I read this: "Swanson introduces *White Premium [b]Turkey[/b] in Water*; I might try the Turkey with Tabby Girl! Thank-u!