There is a lot of confusion when it comes to whole grains. Words like "wheat" and "multi-grain" lead the consumer to believe they are purchasing a healthy whole grain. Grains that are not in their whole state are called refined, and in general they lack the nutritional quality of whole grains.
This picture is a kernel of whole grain. It has three main parts - the endosperm, bran, and germ. The endosperm contains energy in the form of protein and starches; the bran is rich in fiber; and the germ is rich in vitamins and minerals. A refined grain has been stripped of the bran and germ so that only the endosperm remains.
Whole grains are an important source of fiber, vitamin B, iron, antioxidants, and other vitamins and minerals. Studies show that eating a diet that includes whole grains instead of refined reduces the risk of stroke, diabetes, and heart disease by about 30%. Additionally, people who eat whole grains have better weight maintenance.
A general rule of thumb is that a product must say "whole" in front in order to be a whole grain. For example, "whole cornmeal" and "whole wheat" are whole grains; "wheat" is not. There are plenty of exceptions, though! All oats and popcorn are whole grains. Other whole grains include: brown rice (and other colors such as black and red), quinoa, barley, spelt, masa harina, amaranth, and buckwheat.