Grain free food. There are nutritionists who absolutely believe that no dog should be fed grain, cereals or even vegetables. Their argument is that dogs evolved to eat meat, and any plant based foods are mainly in the dog food to add bulk. Dogs have a fairly primitive digestive system, which means a big stomach with one chamber and a short intestinal tract that is ideal for processing animal protein. Some nutritionists believe dog food that contains lots of grain is difficult to digest and can lead to infections, rashes, itchiness, lots of flatulence, loose stools, leaky gut, allergies and obesity. This is because the plant material isn’t actually digested but sits in the dog’s gut until it ferments.