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
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 deficiencyno
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 cultureslong before nutritionists had even thought of the