It appears likely that your pooch's wolf ancestors only tolerated a carniverous diet and didn't have the digestive enzymes needed to handle starch. Scientific studies in Sweden show that, during his evolution from wolf to domestic pet, the dog developed genes that allowed him to digest starch. Humans show similar genetic developments based on increased carb consumption. A shared diet appears to have played a role in bonding man and dog.
Doggy Dietary Needs
The short answer is that starches are not bad for dogs as long as they don't form the majority of the dog's diet. Excessive carbohydrate intake can cause digestive problems and weight gain. Kibble dog food contains some starch, which most dogs tolerate well. You can also give your pooch potatoes and rice. He may even like some pasta occasionally. These starchy foods provide fiber as well as energy. An adult dog only needs protein to form 18 percent of his daily diet. The rest is fiber, carbs, fats, vitamins and minerals.