While some legumes such as peas play a major role in pet food -- included in 54 percent of dry dog and 50 percent of dry cat food recipes -- soybeans play a much smaller role.

Soy -- including soybeans, soybean meal, soybean oil, soy flour and other variations -- is found in 13 percent of dry dog food recipes. Only 10 percent of canned dog food recipes contain soy.

Soy is slightly more common in cat food, being found in 20 percent of dry cat food recipes and 16 percent of wet cat food recipes.

Soy products are more often found in cat food recipes than in dog food.

Soybean meal and soybean oil were the most common forms of soy used in dry dog and cat food recipes, with soy flour the most common form of soy in both dog and cat canned food.