The Role of Plants in Human Nutrition
Plants are the foundation of sound nutrition. The U.S. Department of Agriculture’s Food Pyramid recommends that one consume 6 to 11 servings of whole grains per day: brown rice or whole wheat bread, for example. Modern methods of processing strip the bran and germ, and with them vitamins and minerals, from grains, yielding white rice and white bread. Nutritionists recognize that one should eat the whole grain, including the bran, to obtain optimal nutrients and fiber. Whole grains supply carbohydrates, protein, vitamins, minerals, and little fat. In this group may be added roots and tubers, which supply carbohydrates, vitamins, and minerals, but little protein and fat. Although the quantity is not large, the quality of protein in the potato rivals the protein in egg whites. Orange-fleshed sweet potatoes are rich in beta-carotene, the precursor of vitamin A. The Food Pyramid suggests three to five servings of vegetables. The green leafy vegetables—spinach, Swiss chard, lettuce, and cabbage—contain vitamins and minerals but little protein and fat. The Food Pyramid recommends that a person eat three or four servings of fruit, which supply vitamins and minerals. Citrus fruits have long been renowned as a source of vitamin C. The Food Pyramid includes two or three servings from the meat group, including legumes. Legumes are a source of protein. Although legumes may not supply all essential amino acids, when combined with whole grains they have a balance of amino acids. A dish of beans and rice, for example, supplies all essential amino acids. Nuts, also part of the meat group, supply protein and fat. The sugar from sugarcane or sugar beet supplies calories but no nutrients. Roots, tubers, legumes, and whole grains supply starch. Fruits, vegetables, whole grains, and legumes have fiber. Oil from olives, peanuts, and canola contains monounsaturated fat. Oil from corn, soybeans, and safflower supplies polyunsaturated fat. Coconut oil, palm oil, and cocoa butter have saturated fat.
Leafy greens and yellow- and orange-fleshed roots supply beta-carotene. Seeds and leafy greens contain vitamins E and K. Whole grains, legumes, seeds, and nuts are good sources of thiamine. Whole grains and leafy greens provide riboflavin. Seeds and legumes are rich in niacin. Fruits and leafy greens have vitamin B6. Fruits, seeds, leafy greens, and nuts contain pantothenic acid; legumes, whole grains, and vegetables folic acid; legumes and vegetables biotin; and fruits and vegetables vitamin C. Whole grains, nuts, fruits, vegetables, legumes, and seeds are sources of minerals. Leafy greens and seeds supply calcium, and leafy greens, fruits, legumes, and whole grains contain iron.