The following text is taken from Holistic Guide
for a Healthy Dog, by Wendy Volhard and Kerry Brown. Their
discussion of carbohydrates and the functions they perform seem to
"prove" that most dogs need additional carbohydrates in their diet, a
belief that is very pervasive in most concepts of canine nutrition.
do most dogs really need carbohydrates? In the Waltham Book of Dog
and Cat Nutrition (2nd edition, 1988), we read that
How can this be? Let us discuss just how the dog and cat are able to fulfill their requirement for glucose through a diet of raw meat, bones, and organs.
Carbohydrates do provide quick and easy energy. However, it is not 'carbs' that maintain the health of the organs listed in the quotes above, but glucose. Glucose can be obtained from both fat and protein through a process known as gluconeogenesis, where amino acids and fat (not fatty acids; those use a different cycle) are "converted" to glucose. If carbs are present, though, they will be converted to energy first before fat and protein because they are easier to use. This is the reason that carbs regulate how much starch and fat will be broken down and utilized. If there is a plethora of carbohydrates, fat will be stored instead of used. If there are not enough carbs to fulfill energy needs, then fat will be converted to glucose and used. If no carbs are present, then fat and protein are used to fill energy needs.
Excess carbohydrates are stored in the liver and the muscles as glycogen AND in the body as fat. However, since carboydrates are not the only source of glycogen (which also comes from proteins and fats through a process known as glyconeogenesis), they are not absolutely necessary. Human athletes commonly perform 'carbo loading' techniques where they eat huge carby meals of things like pasta to rapidly replenish their glycogen stores in their muscles and liver before a competition. The carbohydrates, when in excess, are more rapidly converted and stored as glycogen compared to fat and protein. HOWEVER, once again, fat and protein can also be stored as glycogen, which makes carbohydrates unnecessary unless you want to perform 'carbo loading'. I believe it is Purina that has capitalized on this and now has "energy bars" of complex carbohydrates for the canine athlete to help them recover more quickly between events. But, carbohydrates do not rebuild spent muscle tissue, etc. Protein does that. Fat is also easily utilized for quick energy, too, and provides more energy per gram that carbohydrate does.
It is not low carbohydrate intake that causes things like cardiac symptoms and angina; it is low blood glucose. If there is not enough glucose in the blood system, then you run into many problems including black outs, cardiac symptoms (like arrhythmia), and angina (chest pain). Of course, it is interesting that wolves can go without food for weeks and still survive well enough. How do they do that without eating carbs? Simple: they use up fat reserves and may even dip into their own muscle to get the necessary proteins and fats to provide glucose and energy for their bodies. So carbohydrates themselves are not actually necessary; glucose is necessary, and that can be obtained from protein and fat.
What about the brain? The brain is preferentially given glucose above all other organs. Glucose in its ready form, at that. But does this mean carbohydrates are necessary? Since glucose can be had from fat and protein as well, then no.
What about the claim of protein and fat—when converted to energy—weakening the immune system? This seems to be taken from human research where athletes in intensive training had suppressed immune systems which could be improved by consuming proper amounts of carbohydrate. Additionally, white blood cell production in humans seems linked to glucose production. More glucose present means the body is better able to mount an immune response—until there is "too much" glucose around and insulin spikes and starts suppressing all other pathways in the body except for those needed to force the glucose into cells (fat cells). High amounts of simple carbohydrates and sugars are known to suppress the immune system. If this is the case, though, one could wonder how a diet high in grain affects our pets—overstimulation of the immune system due to high concentrations of glucose from the grain? Perhaps this is why many pets suffer "allergies" while on grain!
One other comment I have here is that as long as the animal is receiving appropriate fat and protein, glucose production will not be an issue. And for carnivorous animals like dogs, I cannot help but wonder if their white blood cells are more sensitive to glucose than ours—meaning, less glucose is needed to "stimulate" canine white blood cell (WBC) production compared to human WBC production.
Using protein and fat for energy does not weaken the immune system unless there is not enough to go around, so to speak. If someone is starving, then using protein and fats for energy—while necessary—is a little 'cost-intensive' on the body. But it is not the lack of carbs that is hurting them; it is the simple lack of enough food. Similarly, a human athlete in intensive training may overwork their body to the point that using protein and fats for fuel becomes too cost-intensive to their body.
What about poor hair growth and constant shedding resulting from a lack of carbohydrates? Can these indicate a 'need' for carbs? Maybe, but more likely it indicates a need for better overall nutrition. I personally have NEVER heard of 'carbohydrate deficiency' in any animal. Why? Because there is NO SUCH THING as a "necessary carbohydrate," just necessary glucose. Our bodies, and our dogs' bodies, can do without carbohydrates (although I would say our dogs would fare better than humans, since we are omnivores who do well with fresh vegetables in our diet—except for some cultures that eat mostly meat!). Fats and proteins can be converted easily to necessary glucose. Poor hair growth and constant shedding are linked to an overall poor diet, poor consumption of essential fatty acids, biotin deficiencies, some vitamin and mineral deficiencies, AND a lack of good fats and proteins in the diet. PROTEIN, not carbohydrate, is the building block for hair and skin and all other parts of the body. Carbohydrates do nothing for building and maintaining the body structures except provide easy glucose to fuel the rebuilding process.
What about thyroid function? Thyroid function is dependent upon the correct amount of GLUCOSE produced by the dog's body, not by the correct amount of carbohydrates in the diet. Too much glucose from easily available carbohydrate energy sources can cause just as many problems as not enough glucose. Since we have already established that glucose can be produced from fat and protein, then it would again seem that carbohydrates are actually unnecessary provided that there is enough protein and fat to go around (and a raw diet has PLENTY!).
B compounds, or B vitamins, are found not only in the
intestine (bacteria produce some B vitamins) but also in the meat and
organs of prey animals. Feeding a variety of organ meats as part of a
proper raw diet will cover the B-vitamin requirement quite easily. One
has to wonder: how much of the B compounds in grain and starch and
veggies is actually available to the dog? Compared to something more
bioavailable like liver, then I would say 'not much.'
For further investigation:
(forming glycogen from non-carbohydrate sources)
More on glyconeogenesis