A bit of basic biology may help explain, high carbs can be problematic (this is any carbs, not just grains. Grains add further problems as they are, essentially, grass seeds, and these can cause irritation in many species, including humans, cats and dogs. Dogs don't need any carbs in the diet, they are able to convert protein and fat into the necessary nutrients to keep blood sugar and glycogen levels healthy.Herbivores (Rabbits, Cows, Sheep)
Herbivores eat plants, and their digestive system has adapted to absorb nutrients from plant material.
Grinding Teeth; Herbivores have square, flat molars designed to crush and grind plant material with a sideways motion
Long Digestive Tracts; Plant material is difficult to digest, particularly plant cellulose. The herbivores intestines are up to 10 times longer than their body length, giving the digestive system time to breakdown and absorb correctly.
Digestive Enzymes; Amylase is contained within the saliva of the herbivore combined with the chewing action help to break down the coarse fibre and carbohydrates that makes up plant material. Omnivores (Humans, Pigs, Bears)
Omnivores have evolved to eat both plants and meats hence have adapted their digestive systems
Tearing and Grinding Teeth; Omnivores have sharp canine teeth at the front of the mouth to cater for meat, and flat molars to allow a grinding action for plant material.
Medium Digestive Tracts; Capable of digesting meat based proteins and fats, but still long enough to cater for vegetable matter. (Note that some vegetable which are difficult to digest such as sweet corn can pass through if not chewed correctly)
Digestive Enzymes; As with the herbivore, amylase is contained within the saliva of the omnivore, which also utilises the chewing action to help break down the coarse fibres and carbohydrates that makes up plant material. Carnivores (Cats, Lions, Dogs, Wolves)
Carnivore in Latin means “Meat eater” and the classification refers to diets that consist of mainly meat.
Sharp Tearing Teeth; A carnivores teeth are designed for tearing and slicing (not grinding). Carnivores have elongated front teeth which are used to kill prey and triangular shaped molars which act like a serrated blade and operate in a vertical scissor action to give a cutting action.
Short Digestive Tract; High hydrochloric stomach acid (pH 1-2 compared to humans at a pH of 4-5) quickly digests meat based protein and fat.
Digestive Enzymes; Amylase is not present within the saliva of carnivores hence the burden of digesting carbohydrates is taken by the pancreas. Long term over loading of the pancreas is associated with insulin resistance and ultimately the failure of the pancreas to produce of insulin as found in type II diabetes. Conclusions
Key genetic features of the both dogs and cats classify them as carnivores hence they would have historically eaten a diet almost exclusively of meat
Pointed Teeth designed for grasping ripping and shredding
Jaws designed to swallow whole food (not grinding)
High Acid Stomach Type
Short small intestines
Digestive enzymes adapted to breakdown meat
Absence of enzymes designed to break down vegetable matter http://www.edenpetfoods.com/nutrition/herbivores-omnivores-and-carnivores-explained.html