A grain, let's take rice for example, contains three parts. The parts are the bran, germ, and the endosperm. The bran is the outer hard shell of the grain. It is the part of the grain that provides the most fiber and most of the B vitamins and minerals. The germ is the next layer and is packed with nutrients including essential fatty acids and vitamin E. The endosperm is the soft part in the center of the grain. It contains the starch. Whole grain means that the entire grain kernel is in the food. They are very nutritious.
Refined grains have been processed in a mill to remove the bran and germ. This processing gives the grain a finer texture and improves its shelf life, but it also removes fiber, iron, and vitamins. In other words, refined grains have less fiber and are less nutritious than whole grains. Most grain flours are refined, as is white rice.
Source: Portal Content Development Team