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Proteins |
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Proteins are large molecules that are constructed from different "building blocks" than are carbohydrates and oils. Proteins are formed by combining nitrogen-containing molecules called amino acids. There are about 20 different amino acids, and the type and sequence of the amino acids determines the type of protein molecule. Plants use proteins in several ways: to store energy, as part of their structural framework, and as enzymes. Enzymes are a very important type of protein. Every chemical reaction that takes place in a living organism depends in part on the action of an enzyme. Without enzymes, there would be no metabolism, and no life. The human body can synthesize all but eight of the amino acids it needs. The eight that we cannot make are called the essential amino acids. A dietary deficiency of any one of these amino acids results in a protein deficiency—no matter how much of the other amino acids you ingest. Most plants are deficient in at least one type of essential amino acid. Grains, for example, are an extremely important food source worldwide, but they are generally deficient in the amino acids lysine and tryptophan. Fortunately, legumes have plenty of these amino acids. Most legumes, however, are deficient in the amino acid methionine. Fortunately, grains contain this one. The common advice to strict vegetarians (no meat, eggs or dairy) is to include both grains and legumes regularly in their diets, to be sure they get all the necessary amino acids. It is interesting to note that many ancient and contemporary cultures’ native dishes are based on a grain/legume combination. Examples include corn and beans, or rice and tofu (made from soybeans). This shows the inherent wisdom of these cultures—long before nutritionists had even thought of the "food pyramid."
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