Most dog diets contain a certain percentage of carbohydrates, although they are not considered essential nutrients for dogs. Sugars and starches, which formulate the class of digestible carbohydrates, are metabolized during digestion into glucose. Then glucose provides energy, dispenses amino acids and helps synthesize fats.
Healthy dogs can easily digest cooked starches, while raw starches are more difficult on their systems. After being digested in intestine, carbohydrate will spit into the sugar type which composing them. One of these sugars, lactose (found in milk), is very often not tolerated by adult dogs and will cause diarrhea due to lack of enzyme which digest them. This often called as lactose intolerant. Table sugar (sucrose) or sweets made of sugar are well tolerated by most dogs if fed in small quantities (less than 5% of the total diet).
Carbohydrates which are not used at the time will be stored in the body as glycogen, or animal starch and fat. This excess stored food is often the cause of obesity.
Other form of carbohydrate, fiber, is not essential in a dog's diet and could not be digested. But soluble fibers such as fruit or oat bran play a role in helping maintain proper hydration, in regulating nutrient absorption, and in preserving a healthy intestinal tract. Insoluble fibers, such as wheat bran or cellulose are commonly added to "lite" commercial dog foods to add bulk without adding calories. The same effect may be obtained by adding fresh, raw vegetables such as carrots, broccoli or cauliflower to your dog's diet.