Many commercial dog foods contain grain and meal filler products, including corn, wheat and soy. (dogcare.dailypuppy.com)
In general, commercial dog food can take care of a dog's nutritional needs, but some brands include filler products that can pack on weight without contributing to nutritional value. (roverstayover.net)
This is because of the high content of filler products found in poor dog food brands. (theeverythingdogsite.com)