People commonly think of grains as the primary source of carbohydrates in pet food, however, fruits, legumes and vegetables, among others, are also sources of carbohydrates typically seen in diet formulations.References1.Case LP et al.eople commonly think of grains as the primary source of carbohydrates in pet food, however, fruits, legumes and vegetables, among others, are also sources of carbohydrates typically seen in diet formulations. References1. Case LP et al.