Whole wheat flours contain all three major parts of the wheat kernel,

Bran

• Bran is the hard, brownish outer protective skin of the grain. It surrounds germ and the endosperm, protecting the grain from weather, insects, mold, and bacteria.
• The bran consists of 7 layers. The bran layers are a concentrated source of dietary fiber.
• The aleurone layer is the largest portion of the bran, constituting 75% or more of its dry weight.
• The aleurone layer is a concentrated source of vitamins, minerals and other nutrients.

Endosperm

• The endosperm is the inner part of the grain. It supplies food to the growing seedling.
• The main nutrients in the endosperm are protein and carbohydrate. About 50 to 75% of the endosperm is starch. It also contains storage proteins, typically 8 to 18%. Relatively few vitamins, minerals, fiber, or phytochemicals are found in the endosperm.
• White flour is produced from the endosperm.

Germ

• The germ contains the plant embryo. It typically accounts for about 2 to 3% of the wheat's dry weight.
• Most of the wheat kernel's fat and vitamin E content is found in the germ.