The pet food industry does not formally define fillers. Critics use the term for ingredients like corn hulls, wheat middlings, and cellulose that provide fiber or carbohydrate energy but limited essential amino acids. However, some ingredients labeled as fillers serve real purposes: beet pulp provides beneficial prebiotic fiber, and rice is a highly digestible carbohydrate source for sensitive stomachs. Rather than fixating on filler lists, evaluate the overall ingredient panel: named animal proteins should appear early, the food should meet AAFCO standards, and your pet should maintain healthy weight, coat, and stool quality. A veterinary nutritionist can help distinguish marketing claims from genuine quality concerns in your pet's specific diet.