Most flour is ground cereal or grain, such as wheat, and is primarily a source of starch or carbohydrates in the diet. Carbohydrates in flour can be simple (converting quickly to sugar during metabolism), complex or fibrous, depending upon the type of flour. In addition, flours contain varying amounts of fat and protein as well as fiber, which all slow the absorption rate of the carbohydrates and add to nutritional value.
White Wheat Flour
According to R. L Duyff, writing for the American Dietetic Association, white enriched flour is used in 80 percent of baked goods. This flour is processed so that most fiber and nutrients are lost, though some nutrients (iron, thiamin, riboflavin and niacin) are added in the enriching process. According to "The Complete Food Count Guide," white flour contains about 19g carbohydrates per 1/4 cup with only 0.75g fiber, 0.25g fat, and 3.25g protein. Unbleached and bleached white flour contain the same nutrients; only the color is different.
Whole Wheat/Rye Flour
Whole wheat flour contains the bran and germ of the wheat, so it is higher in fiber and protein than white flour, making it heavier in texture and more nutritious, with a nutty flavor. It contains about 20g carbohydrates per one-quarter cup with 3g fiber, 0.5g fat and 4g protein.
Whole grain rye flour has a distinctive flavor and is slightly heavier in texture than whole wheat flour because of increased fiber. Rye flour contains about 23g carbohydrate per 1/4 cup with 4g fiber, 0.5g fat and 3g protein.
Rice flour is similar to white flour in nutritional value but is gluten-free, so people with wheat sensitivity can use rice flour. The finely ground flour has even less fiber and contains 19g carbohydrates per 1/4 cup with 0.6g fiber, 0.125g fat, and 2g protein.
Buckwheat flour is not wheat as it's actually made from buckwheat groats (the hulled portion), so it is gluten-free and high in fiber and nutrition. This dark flour has a strong flavor and heavy texture, so it is often mixed with other flours. Buckwheat flour contains 20g carbohydrates per 1/4 cup, with 6g fiber, 1.5g fat, and 5g protein.
Gluten flour is made from the wheat berry, so it is very high in protein and adds elasticity and volume to breads. Bread flour, for example, has added amounts of gluten already in it. Using about 2 tbsp. of gluten flour in a recipe for bread, especially with whole wheat or other heavy flour, helps to create a lighter dough while adding protein. Gluten flour contains only 6g carbohydrate per 1/4 cup but no fiber, 0.5g fat and 23g protein.
Soy flour is made from raw soybeans, so it is gluten-free. This flour is low in carbohydrates and high in protein, so it can replace up to 30 percent of other flours in bread recipes to increase nutrition. If more is used, the bread won't rise properly because bread needs gluten for volume. Soy flour contains 8g carbohydrate per 1/4 cup with 3g fiber, 1g fat and 10g protein.