The Truth Behind Some Commonly Held Nutrition Notions

Is Corn Bad?

With advertisements for pet foods touting, they “never use corn,” “No corn,” and “corn is not an ingredient in our dog food,” the implication is that corn is bad in pet foods. These arguments seem to be based on three ideas—that corn is poorly digested, corn is a cheap filler, and corn is a common allergen. But what is the truth behind this commonly held nutrition notion?

Corn is Not Poorly Digested

The digestibility of corn is perhaps the most researched topic in pet nutrition. Studies in which dogs were fed dry food diets with corn and other carbohydrate sources found starch digestion was almost complete {>98%) in dogs’ small intestine and was unaffected by carbohydrate source (1). Notably, in one of these studies peas and legumes (two alternatives to corn in “corn-free” diets) were actually less digestible than corn (2). Similar studies for cats found digestibility of >93% for all diets studied, indicating that even carnivores like cats can efficiently digest corn when it is processed into kibble (3). Although the digestibility of corn is well-researched, research on the digestibility of other carbohydrate sources used in some “corn-free” diets is limited.

Corn is Not a Cheap Filler

Dry cat and dog foods require starches from carbohydrates for the food to be formed into kibble. Corn is one carbohydrate that provides this function in dry pet foods. Based on information from commodities markets, while corn is less expensive than meats, as far as carbohydrates are concerned, it is not cheap. Consider this: Corn has doubled in price per bushel over the past year. Corn is on track to exceed wheat in price per bushel for the first time since 1996. Corn and wheat are nearly twice the bushel price of oats (a carbohydrate used in “corn-free” foods) (4). Corn is not a “filler”—an ingredient with no nutritional purpose in a food. Corn provides some protein (about average when compared to other grains), antioxidants to protect against damage from free radicals, and fatty acids essential for healthy skin and coat.

Corn is Not a Common Allergen

While there have been some documented cases of corn allergies in dogs, these cases are few and far between. Corn is seldom an allergen in dogs or cats. A review of seven studies found the top food allergens in dogs were (in order) beef, dairy, wheat, egg, chicken, lamb, and soy. Similarly, a review of 15 studies from 1967-2004 found that beef, dairy, and wheat together accounted for 69% of reported cases of food allergens in dogs, with lamb, egg, chicken and soy accounting for another 25% of the cases. Furthermore, a review of 200 confirmed cases of canine food allergies revealed only 3 (1.5%) were caused by corn—the same number as caused by rice. Similar research exists for cats–a review of seven studies on food allergies in cats found the top allergens were beef, dairy, fish, and lamb, with beef, dairy and fish accounting for the vast majority (80%) of cases reported from 1967- 2001 (5).

Corn is simply not a common food allergen for dogs or cats. And, even if it was, that doesn’t mean it shouldn’t be in dog or cat foods. For instance, the top food allergens in people are eggs, fish, milk, peanuts, shellfish, soy, tree nuts, and wheat. While people with food allergies certainly should avoid the ingredients to which they are allergic, many nutritionists recommend these common “allergens” be included as part of a normal healthy diet.

So, is corn bad? No, not as an ingredient in pet foods. But it is bad as part of a corny joke…

Bad Corny Joke

An ear of corn walks into a bar and says to the bartender, “Can I have a beer?” The bartender replies, “No, we don’t serve food here.”

Select References:

1. Journal of Nutrition 1994
2. Journal of Animal Physiology and Animal Nutrition 2004
3. Journal of Animal Science 2008
4. Data from commodities markets, accessed April 2011.
5. 5. Small Animal Clinical Nutrition 2010