What Is Complete Protein? We hear it said that the quality of protein in meat is higher than in vegetable sources, or that meat contains complete protein whereas plants do not. What is meant by these terms? Twenty amino acids make up the proteins our bodies use. Of these twenty, eight must come from the food we eat. These eight are called the essential amino acids. The rest our bodies can synthesize. All the essential amino acids must be present simultaneously and in proper proportions for our bodies to utilize them. If one is lacking, even temporarily, the body’s ability to build protein will fall accordingly. Complete protein foods contain all eight essential amino acids. Animal products—eggs, milk, and meat—provide all eight amino acids in the proportions our bodies require. Eggs most nearly match the ideal pattern. Milk is a close second, and meats follow. Soybeans and whole rice come close to meats in protein quality. Other grains, legumes, seeds, and nuts are good sources of protein but each lacks one or more of the essential amino acids. Amino Acid Teamwork The amino acid deficiency in plant proteins does not mean that we must rely on animal products only for a complete protein supply. The amino acids lacking in one plant source can be made up in another. Plant proteins complement each other. But how do we know what complements what? Actually the relationships are not hard to remember. Food habits from all over the world attest to the intuitive skill in combining complementary amino acids. Chart A on page 32 shows how it works. In terms of specific amino acids, milk contains protein rich in lysine; legumes generally are low in tryptophan and sulfur-containing amino acids and, like milk, high in lysine. Grains are low in isoleucine and lysine. Thus milk and/or legumes complement grains.8 Seeds such as sunflower and sesame could be listed with grains since they are also complemented by milk and legumes. Most people, however, don’t eat enough seeds to consider them an important source of protein. Diet for a Small Planet, a book focusing on the age-old practice of complementing proteins, says: “Eating a mixture of protein sources can increase the protein value of the meal; here’s a case where the whole is greater than the sum of its parts ... such mixes do not result in a perfect protein that is fully usable by the body (remember that only egg is near perfect). But combinations can increase the protein quality as much as fifty percent above the average of the items eaten separately.”9 In our terms, this means getting more with less as we plan menus involving plant protein. Chart A on page 32 gives menu combinations that show proteins in complementary relationship. Some of our most common are cereal with milk, cheese sandwiches, and bread with milk. These are typical of a European background where grains and dairy products make up an important part of the diet. Other parts of the world have prepared nutritious combinations for centuries. Latin Americans eat rice with beans or beans with corn. In India a pea or lentil puree (dhal) is eaten over rice. In Indonesia fermented soybean cakes (tempe) go with the rice meal. A mung bean-rice cereal is a popular Vietnamese breakfast. The Chinese and Japanese use bean noodles, bean curd, and bean sprouts with rice. Rice-lentil mixtures complemented by yogurt are common in the Middle East. Cornmeal mush eaten with beans is a staple in many African countries. We can keep using our own well-known cereal-milk combination and borrow from other traditions for a more interesting and responsible diet. Complementary foods, to provide maximum usable protein, must be eaten together at the same meal. Chart A on page 32 shows complementary proportions that result in efficient use of plant proteins. These proportions do not have to be followed slavishly in one meal. They are given to show what good proportions are realistic for the way we prepare food. More With Less 43