Whole grains are considered an important part of a healthy diet because research suggests that many of nutrients they contain are beneficial to the health. Whole grains may protects against cardiovascular disease, gastrointestinal ill health, cancer, diabetes, as well as aid in maintaining the correct body weight. To be defined as a whole grain, the starchy endosperm, germ and bran of the grain must all be present in the food in the same relative proportions as they exist in the intact grain on the plant. Many nutrients are present in grains, and these nutrients interact in a synergistic way such that their combined benefit is greater then the sum of the individual nutrients. The average Western diet tends to comprise mainly of refined grains, whereas the diets of those from developing countries tends to contain mainly whole grains.
The bran is a tough outer layer that protects the germ and endosperm from sunlight, pests, water, disease and other environmental damage. The bran is a rich source of vitamins and minerals (such as magnesium and vitamin B), phenolic compounds as well as insoluble fibre (such as cellulose and hemicellulose). The endosperm makes up the largest part of the whole grain, and is rich in digestible carbohydrate (starch; amylase and amylopectin), vitamins and minerals as well as having a relatively high protein content. The endosperm is a provider of energy for the germ during initial growth. The germ part of the wholegrain is the embryo of the plant and in the right conditions will form a new plant, using the endosperm as an initial source of energy. The germ contains vitamins, minerals, protein and fat.
Consumption of refined white flour has been shown to result in increases in degenerative disease rates when introduced to native societies not previously exposed. During refining of the whole grain to white flour, the outer bran and inner germ layers are removed and discarded. Only the endosperm is processed, and so many of the vital phytonutrients from the whole grain are not present in refined white flour. From the outer bran layer, the non-digestible, insoluble, poorly fermentable carbohydrates which include cellulose, hemicellulose and arabinoxylan are lost. From the inner germ various soluble fibres, fermentable oligosaccharides, resistant starch, lignans, vitamins, minerals, polyphenols and oils are also lost in the refining process. It has been estimated that the whole grain contain roughly 80 % more dietary fibre than the refined equivalents. Therefore whole grains should be eaten in preference to refined grains wherever possible.
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