In order to determine what our dogs should be eating, we need to look at what they are designed to digest and how their bodies will naturally gain nutrients. If we look at a dog's digestive physiology, it is essentially identical to that of wild canids. Key points being dentition, digestive tract length, stomach acidity, production of digestive enzymes, rate of flow, and bacterial populations. By digestive standards, dogs are carnivores. Everything about them was designed to eat raw meat and bones. Now, please do not read the word "raw" in there and think that I am staunchy promoting a raw diet. Yes, I feed my dogs a raw diet, but I understand that some people are not willing or able to do so for their dogs, for whatever reason.
But regardless of what you do or don't/will or won't feed, the truth of the matter is that our dogs are carnivores (who also happen to have a sweet tooth so enjoy indulging in treats like berries, fruits, marshmallows and ice cream).
The idea that "natural is better" is based on the diea that in order for a whole body to be healthy as possible, the fewest stresses should be applied to that system as possible. Going to extremes, if a dog is fed a vegan diet, we are expecting their digestive tract, their "system", to strip nutrients from food matter that they were not designed to eat. They do not have the digestive enzymes or bacterial populations required to digest plant matter. Obligate herbivores rely on immense populations of bacteria in their rumens or ceca to digest plant matter for them, then the herbivores gain their nutrients from the by-products produced by the bacteria during the digestion of that plant matter. So even cows do not digest corn for nutrition, rather, they ingest corn which is digested by bacteria in the rumen. That bacteria gives off volatile fatty acids as they process the plant matter, and the VFAs get absorbed by the cow's intestinal lining to be used as energy. If we expect our carnivore dogs to do that same thing, we are asking their digestive system to work THAT much harder to try and leech nutrients from matter it can't digest. We are promoting unnatural bacterial growth, overproduction of digestive enzymes and harder working of the system as a whole. Like any machine, run it too hard for too long and it will wear out.
Less extreme, but same basic idea, is asking a dog to get nutrition from a grain based diet. Or, add to it, a processed diet.
During the processing of commercial foods, great amounts of heat are used. During heating, proteins are denatured and folded in different manners. The digestive enzymes that a dog produces naturally rely on natural "raw" folding of proteins in order to act effectively on them and tear them apart into amino acids, used for nutrition. If those proteins are folded differently due to denaturation (from heating), then the efficiency of the digestive enzymes is reduced, requiring increased production of enzymes and the system working harder as a whole.
Again, it all leads back to more stress being applied to the overall system, wearing it out sooner, making it work in ways that it was not designed to work.
During the formulation of "vet recommended" diets (Hills, SD, Metacal, Walthams, etc.), the key aspect during production is meeting preset nutritional guidelines. ie. How much protein, fat, and carbs does a dog need? What levels of vitamin A, iron, zinc, etc. AND, how can those levels be met in the most cost effective way? By taking the by-products of human consumption (grain fractions, meat by-products, etc.), we can get close to those numbers. Then heat it all and the numbers decrease, so you add synthetic vitamins and minerals to bring the numbers back up again. Yes, vet diets meet the nutitional needs of dogs. No doubt. They have all the vitamins, minerals, and nutrients that a dog needs to survive. But what they do NOT take into consideration is the process by which dogs most easily acquire those nutrients. The extra work that the carnivore's digestive tract has to put in in order to strip those nutrients from ingredients that it was not designed to handle.
The key to determining what a dog should eat is to look at what it is designed to eat. What does the physiology say?
