Many years ago, did you know that dogs and humans ate a diet consisting of 4% carbohydrates? And did you also know that today, we both eat about 40% grains and starches? I found that to be very interesting because that exact change coincides with American's levels of obesity and diabetes. It also matches the same issues with dogs.
You may not know this, but dogs have four enzymes that naturally increase blood sugar levels to provide them energy and only one to lower it; insulin. Guess which works the hardest. It's insulin. Why, because more and more dogs are fed kibble. And if you read the label you may see sugar, corn syrup, high fructose corn syrup, dextran, maltodextrin, dextrose, fructose, glucose... you can see all 56 here: http://www.womenshealthmag.com/food/different-names-for-sugar Yes, 56 names for sugar.
What does this mean? Insulin should never have to lower blood sugar in a dog. They have four enzymes that actually work to manufacture blood sugar. Grains and starches should make up about 4% of a dog's diet, not 40% (people too :). A dog can produce its own vitamin C too (just a raw dog fun fact). A grain free diet is a marketing myth. A dog's food needs to be both grain and starch free; or at least no more than 4%. It means if it comes in a bag it has grains, starches, or both. READ THE LABEL and educate yourself to what your feed yourself and your dog.