Is plant protein enough?

If you're worried about getting enough protein on a vegetarian diet, don't be. Since proteins are in practically every food we eat, from apples to tacos, getting adequate protein on a vegetarian diet is easy.

For years people have considered protein the most important ingredient in food, necessary for life, growth, and musstrength. That's probably why the Greek word proteos, meaning primary or taking first place, was used to name it

Food protein is important to the body because it's made up of nitrogen-containing amino acids. Think of them as building blocks that the body uses for a whole host of essential functions, such as making skin, nails, hair, muscle, bone, connective tissue, and cell membranes. Food protein is also needed to make vital hormones, important brain chemicals, antibodies, digestive enzymes, and necessary elements for the manufacture of DNA. And it's an alternate energy source when other energy sources are in short supply.

NINE ARE ESSENTIAL. Every protein in both plant and animal foods has its own unique structure, composition, and properties. And each protein has a unique amino acid pattern. Altogether, there are about 20 different amino acids needed for human life. Of these, nine are classified as essential since the body cannot manufacture them in sufficient quantity for normal body functions. This means that the nine must be obtained from the diet. Optimal health depends upon an adequate supply of these essential amino acids.

The quality of a protein depends upon the relative amounts of each one of the essential amino acids. Animal proteins usually have a better balance of the amino acids than do plant proteins. However, a mixture of plant proteins can provide that balance.

In other words, a relative deficiency of an amino acid from one plant protein can be made up by the amino acids from another plant protein. In fact, the intake of the nine essential amino acids by vegetarians is normally well above the recommended daily intake for each of the amino acids.

IT'S THE COMBINATION THAT COUNTS.

It is now generally recognized that a plant-based diet can meet the body's need for the essential amino acids, provided that various unrefined grains, legumes, nuts, and vegetables are eaten regularly. It's important that whole-grains be used, rather than refined grains, because the protein quality of a grain is reduced significantly when it is refined. For example, the protein quality of white flour is 22 percent less than that of whole-wheat.

Asparagus and broccoli have few calories; however, the protein in them accounts for about 35 to 40 percent of those calories. While green vegetables contain only small amounts of calories and protein, the protein in them is of a good quality, similar to that in grains and legumes.

COMMON FOOD COMBINATIONS.

Cereals tend to be low in the amino acid called lysine but adequate in the sulphur containing amino acid methionine. Legumes are adequate in lysine but low in methionine. Therefore, the amino acid profiles of the cereals and legumes complement each other so that a cereal-legume combination provides high-quality protein.

Many cultures of the world rely upon a cereal-legume combination to provide a major portion of their energy supply. Examples of these food combinations would include maize and beans in Latin America, millet and groundnuts in the African Sahel, rice and soybeans in Southeast Asia, wheat and garbanzos in the Middle East, rice and dahl in india, and cornbread and black-eyed peas in the southern United States.

For the different types of protein to complement each other, they must be eaten during the same day, but not necessarily within the same meal. This allows for flexibility in food preferences and removes the concern about whether each meal contains properly balanced protein sources.

SOY IS UNIQUE. Soy is a plant protein with a difference. Experiments in Boston with young college students who were fed diets containing different proteins sources showed that soy protein is of high nutritional quality and is capable of providing adequate amounts of all essential emino acids. Soy protein was able to maintain a nitrogen balance similar to that achieved when using any one of three animal proteins-meat, milk, or egg.

This means that no matter which of the four protein sources (soy, meat, milk, egg) the students were fed, they were able to retain more protein than they lost. Clearly, the amino acid profile of soy protein compares favorably to that of the animal proteins, and there is need to supplement soy with any other plant proteins.

HOW MUCH DO WE NEED? Protein requirements depend upon many factors, such as a person's body size, age, rate of growth, and the quality of the protein. Pregnant and lactating women require additional protein because of the growth and development of the child.

The number of calories a person eats is also important, since an adequate intake of energy allows for nitrogen retention. Insufficient caloric intake means that protein must be metabolized or burned for energy.

Some people are concerned that they may not get sufficient protein unless they eat protein-rich animal foods. Although nonvegetarian diets typically provide more protein, vegetarian diets are still able to meet an exceed the recomended daily allowance (RDA) requirements. This includes the average protein intake of both lacto-ovovegetarians (those who use eggs and dairy products, but no meat, fish, or poltry) and vegans (total vegetarians who use no animal products at all).

PLANT FOODS DO THE JOB. The RDA for protein for adult men and women is about two ounces of protein per day. the protein requirement corresponds to about 9 percent of an adult's total daily caloric intake. The protein in cereal grains, such as wheat, oats, and rice, represents about 8 to 12 percent of the total calories of these foods. Legumes average about 20 to 30 percent of their calories as protein. So a mixed cereal-legume-based diet can provide at least 10 percent of the calories from protein.

Thirty-five years ago Dr. Mark Hegsted of Harvard University actually showed that if plant foods were selected carefully, only about one ounce of protein per day would be sufficient to meet protein needs. The true requirement for protein is quite small and can easily be met by simple, nutritious everyday foods.

TOO MUCH CAN HURT. A number of advantages can be associated with the use of plant proteins. The lower protein intake of vegetarian diets may be beneficial, since an excess of protein can contribute to flushing calcium out of the body through the urine, increasing the risk of osteoporosis. Also, excess protein can decrease kidney function in persons with previous kidney damage.

Furthermore, the requirements for many vitamins and minerals are increased with a high-protein diet. The use of animal protein is also associated with an increased intake of saturated fat and cholesterol. The negative effect of this on cardiovascular health is discussed elsewhere in this magazine.

We can safely say that a vegetarian diet can meet the protein needs of healthy individuals, provided that the diet contains an adequate level of calories and that it consists of a variety of unrefined plant foods. Dietary surveys confirm that vegetarian diets contain both the quantity and quality of protein to maintain optimal health.

Winston J. Craig, PhD., R.D., is professor of nutrition at Andrews University, Berrien Springs, Michigan.