Refined carbohydrates tend to be much in lower in fiber and vitamins than whole grains. These are complex carbs that have had fiber removed from them leaving reproduce simple carbohydrates. These are rapidly absorbed causing a blood sugar increase, which is followed by some crash. During the milling process, the germ and bran is peeled and the grain's endosperm is crushed. The final product becomes easier to gnaw and digest. The main reason manufacturers process the grain is to lengthen shell life.
