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Vezels

Voordelen van voedingswaarde van volkoren (English)

The refining of grains strips out a sizable portion of their nutrition, so whole grains have the advantage, especially when it comes to vitamins, minerals, fiber and phytonutrients. According to FDA and the American Association of Cereal Chemists International, St. Paul, MN, whole grains are defined as "intact, ground, cracked or flaked fruit of the grain whose principal components, the starchy endosperm, germ and bran, are present in the same relative proportions as they exist in the intact grain." Whole grains can undergo processing and reconstitution and still be considered whole grains if they contain the same proportion of bran, germ and endosperm as the original grain before processing.

Nutrient content
Insoluble, poorly fermentable carbohydrates make up the majority of the outer bran layer of a whole grain, whereas the inner germ contains soluble fibers, vitamins, minerals, polyphenols, oils and other phytonutrients. During refining, the outer bran layer and inner germ layer are partially or fully removed and, therefore, fiber, vitamins, minerals and phytonutrients are lost. Even though refined grains are enriched with thiamin, riboflavin, niacin, folic acid and iron to restore levels back to those in the original whole grains, vitamin E, trace minerals, unsaturated fat and phytochemicals are not replaced. Therefore, "whole grains have 2.5 to 5.0 times more nutrients than refined grains," notes Cynthia Harriman, director of food and nutrition strategies, Oldways/The Whole Grains Council, Boston.

Whole grains include commonly consumed grains such as whole wheat, wild rice, brown rice, whole oats and oatmeal, whole-grain cornmeal, and popcorn, as well as whole rye, whole-grain barley, buckwheat, triticale, bulgur (cracked wheat), millet, quinoa, sorghum, amaranth, emmer, farro, grano (lightly pearled wheat), spelt and wheat berries.

Unique whole-grain nutrients
In addition to fiber, vitamins and minerals, whole grains contain a number of other beneficial nutrients. Whole grains are a source of antioxidants, including lignans, carotenoids, lutein, zeaxanthin and ß-cryptoxanthin. The germ fraction of whole grains also contains vitamin E in the form of tocopherols and tocotrienols (Critical Reviews in Food Science, 2010; 50:193-208). And, the fat in whole grains comes primarily from oleic acid and the essential omega-6 fatty acid linoleic acid. Whole grains also are a source of resistant starch, which affects colonic bacteria and may increase satiety, prebiotic oligosaccharides and lignans (PLoS One, 2010; 5:e15,046; Nutrition Research, 2009; 29:100-105; Critical Reviews in Food Science and Nutrition, 2011; 51:178-194). And finally, whole grains are a source of plant sterols and stanols, compounds that inhibit the body's absorption of cholesterol (Asia Pacific Journal of Clinical Nutrition, 2009; 18:179-186).

Each whole grain has a different nutrition makeup and their fiber content can vary widely. For instance, brown rice contains 0.6 grams fiber per 16 grams brown rice, whereas Kamut® grain contains 3.9 grams of fiber per 16 grams. Despite these differences, the health-promoting effects of whole grains are not solely due to their fiber content.

In addition to varying amounts of fiber, the total antioxidant capacity differs among grains. "Corn has one of the highest antioxidant activities, followed by wheat, oats and rice," says Harriman. In a study examining the distribution of phytochemicals in wheat, scientists milled two varieties of wheat into endosperm and bran and germ fractions to examine how the refining process affects the total phytochemical content. The total phenolic content of bran and germ fractions was 15 to 18 fold higher than that of the endosperm fractions. And, the bran and germ fraction, the part that is removed during the refining process, contained an average of four times more lutein and 12 times more zeaxanthin, antioxidants found in the retina of the eye. The bran and germ fraction also contributed to 83% of the total phenolic content, 79% of the total flavonoid content, 85% of the total hydrophilic antioxidant activity and 94% of the total lipophilic antioxidant activity (Journal of Agricultural and Food Chemistry, 2005; 53:2,297-2,306; Archives of Biochemistry and Biophysics, 2007; 458:128-135). Though whole grains retain more antioxidants, thermal processing and milling can make some of the insoluble bound phytochemicals found in grains more bioaccessible (The Journal of Nutrition, 2011; 141:1,011S-1,022S).

Whole-grain health claims
The FDA approved health claim for whole grains and risk of heart disease and certain cancers specifies that the food contain 51% or more whole-grain ingredients by weight per RACC (reference amounts customarily consumed) and a dietary fiber content of at least:

• 3.0 grams per RACC of 55 grams

• 2.8 grams per RACC of 50 grams

• 2.5 grams per RACC of 45 grams

• 1.7 grams per RACC of 35 grams

Additionally, the food must be low fat. The required wording for the claim is: "Diets rich in whole grain foods and other plant foods and low in total fat, saturated fat, and cholesterol may reduce the risk of heart disease and some cancers.".

Gaining ground
Many whole grains are gaining popularity yet don't come in a refined form. Quinoa is a naturally gluten-free grain that contains more protein than many grains, and one- quarter cup, uncooked, is an excellent source of magnesium and iron, and a good source of copper and phosphorus. In addition to quinoa, food manufacturers and chefs are incorporating a variety of other, less commonly used grains into food to enhance the taste and texture of products while meeting consumer needs (like gluten-free or nonallergenic).

According to NHANES data, many Americans are falling short on their intake of whole grains. This presents an opportunity for food manufacturers to create products that incorporate one or more whole grains while also communicating the nutrition benefits of whole grains to consumers. As Harriman notes, "it all comes down to a balanced diet incorporating a variety of nutrient-rich foods for good health."

Marie Spano, M.S., R.D., CSCS, is a nutrition communications expert whose work has appeared in popular press magazines, e-zines and nutrition-industry trade publications. She has been an expert guest on NBC, ABC and CBS affiliates on the East Coast. For more information, visit mariespano.com.

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