Grains come in many shapes and sizes, from large kernels of popcorn to small quinoa seeds. Also called cereals, grains are the widely varied seeds of grasses, which are cultivated for food.

All types of grains are good sources of complex carbohydrates, various vitamins and minerals and are naturally low in fat. But grains that haven't been refined — called whole grains — are even better for you. Whole grains are better sources of fiber and other important nutrients, such as selenium, potassium and magnesium.

Anatomy of a whole grain

Grains are the seeds of plants. When whole, they include the bran, germ and endosperm — all of which contain valuable nutrients.

·         Bran. Forming the outer layer of the seed, the bran is a rich source of niacin, thiamin, riboflavin, magnesium, phosphorus, iron and zinc. The bran also contains most of the seed's fiber.

·         Germ. The part from which a new plant sprouts, the germ is a concentrated source of niacin, thiamin, riboflavin, vitamin E, magnesium, phosphorus, iron and zinc. The germ also contains protein and some fat.

·         Endosperm. Also called the kernel, the endosperm makes up the bulk of the seed. It contains most of the grain's protein and carbohydrates and has small amounts of vitamins and minerals.