Lets talk about what is important in solid canine nutrition. It is important to note, that, unlike people who vary their diets each day, dogs get basically the same entree twice a day, often for life. This makes it vital that we do not feed a food with chemical preservatives, harsh fillers, etc. It also makes it important that they get a truly balanced diet in all aspects. Giving your dog a food with one carbohydrate, even a nutritionally sound carbohydrates, is not as beneficial as balanced carbohydrates.
Dogs are much the same.
When they eat the stomach of their prey, they are getting a variety of grains, among other things. Balanced carbohydrates, fats, and proteins will make up a much healthier, long term diet for your dog. It is also important that we talk about the quality of protein used in your dog's food. Manufacturers have learned to get the numbers right without much regard for digestibility. What the label doesn't say is the quality of protein that they use to get to the magic numbers.