What's the problem with refined grains?

When it comes to grains, most people also eat far too many refined grains. Extensive processing of grains can leave very little in the way of nutritional value. It can also leave grain products that are rich in the simpler carbohydrates and elevate blood sugar levels in a problematic way. Refined grain flours are usually defined in terms of "percent extraction." Wheat flour is 60% extraction when only 60% of the original whole grain remains in the flour, and the other 40% has been removed. Most of the wheat flour products in the United States have been made from 60% extraction flour. Unfortunately, over half of the original nutrients in whole wheat are lost from 60% extraction flour because extraction involves the removal of the germ and bran, which are the primary sites for nutrient storage in the grain. There is absolutely no doubt in my mind that refined grain products cannot serve as the basis of a healthy diet.

George Matlin