The function of carbohydrates in pet food. The value of carbohydrates in dog foods is often debated among nutritionists. Despite the debate, most commercial dry foods contain between 30% and 70% carbohydrates.he function of carbohydrates in pet food. The value of carbohydrates in dog foods is often debated among nutritionists. Despite the debate, most commercial dry foods contain between 30% and 70% carbohydrates.