Whole grains, as opposed to processed, "refined" grains, contain all three parts of the grain: the bran, the endosperm and the germ. The bran – the outer layer – is full of fiber, B vitamins, 50 to 80 percent of the grain's minerals and other nutritious plant substances known as phytochemicals. The endosperm - the starchy part of the seed – contains complex carbohydrates, proteins, and smaller amounts of B vitamins. The germ is full of B vitamins, vitamin E, trace minerals, healthy kinds of fats, and additional phytochemicals and antioxidants. Different grains vary in the types and proportions of all these nutrients.
Refined grain products lack the bran and germ of the grain. The processing reduces the nutrient content of the original whole grain by 25 to 90 percent. Most refined grain foods are "enriched" but with only a fraction of the nutrients lost in processing.
Refined grain products have not only been stripped of valuable nutrients including most if not all the dietary fiber; their predominance in the American diet has given carbohydrates a bad name. Low-carb diets have been the rage, in competition with very low fat diets, but that's all changing. The human body requires protein, fat and carbohydrates to function properly, and we now know more about what constitutes "healthy fats" and "healthy carbohydrates." Whole grains are an excellent source of healthy complex carbohydrates.
The difference between "stripped down carbs" and whole grains is the nutrient content and glycemic effect - the effect on blood glucose (or blood sugar). Protein, fiber and fats all have a modifying effect on the glycemic load of foods. Foods that are highly processed and composed of little more than starch and/or sugar generally tend to cause rapid fluctuations in blood sugar, in comparison to whole grains which contain protein, fiber and healthy fats that help keep blood sugar more steady. Overconsumption of mostly refined carbohydrates is associated with obesity and insulin resistance (IR), where the body's cells become resistant to insulin's attempts to usher glucose from blood into cells where it is needed. The result is abnormally high blood sugar and insulin levels. IR in turn sets the stage for type 2 diabetes and a host of other health problems.
The dietary fiber in whole grains deserves emphasis. Not only does fiber help to regulate blood sugar; soluble fiber (found especially in oats and barley) helps lower "bad" cholesterol in the blood, and insoluble fiber is essential to digestive health
Years of medical research have confirmed that including at least three servings of whole grains daily reduces the risk of heart disease, stroke, cancer, diabetes and obesity. Few foods offer so many benefits.