The dog's natural need for nutrients
By nature, the dog, like its cousin the wolf, is a predator – a hunter and carnivore. Physiologically speaking, it is adapted to a diet consisting of animal fat and protein. Carbohydrates do not, or very little, form part of its diet.
The dog's digestive system, like other carnivores, has typical functions that are intended for its natural diet. As with other predators, the dog also has a large stomach, because a long time can pass between each time a prey is taken down.
The digestive system is simple and short and adapted to the digestion of energy-rich food.
The dog has a set of teeth - large canines and pointed molars - which are used to tear large pieces of meat and crush bones.
The dog does not have amylase in its saliva. Amylase breaks down carbohydrates in food into smaller molecules. Animals adapted to a vegetarian diet have amylase in their saliva, so the breakdown of carbohydrates can start early.
Absorption of nutrients through the intestinal wall occurs in the small intestine. The large intestine is short and has little fermentation activity. The microflora in the colon will supply itself with the nutrients that are in excess, but the breakdown rate of fiber is low.
The dog uses fat as an energy source very well and is also adapted to a protein-rich diet.
However, most dog food on the market today is grain-based and very high in carbohydrate, both in the form of starch and fiber. Dog food mostly contains moderate amounts of fat and both vegetable and animal protein sources are used. Dog food is also often highly processed. Rumen and dog food are very rich in protein and fat derived from animal ingredients.