Starch digestion takes place in three stages. The first stage takes place in the presence of an enzyme called alpha amylase. In a dog, this amylase protein is present in its intestine. However in a human, this enzyme is present in the Saliva in the mouth. This salivary enzyme is also called Ptyalin. Chewing food well is important as Ptyalin does not act well in the acidic environment in the stomach. A pancreatic enzyme takes over the action in the stomach. Human digestion in this regard is very close to that of vegetarian mammals. Just from the fact that dogs have the Ptyalin enzyme in their intestine while humans have them in their mouths points to a vegetarian diet need of a human.
Another interesting factor is that the levels of Ptyalin vary between ethnic groups. Asians have higher levels of Ptyalin than Europeans. However, the strong signature of Ptyalin in humans is strong enough to indicate a vegetarian orientation of human evolution. Just like specific genes got switched on during the evolution from a wolf to a dog, humans genes related to carbohydrate digestion is also an evolutionary miracle. This brings one more perspective in one’s personal decision to be a herbivore.