Facts About Protein

This article discusses facts on protein. Protein is unquestionably the most important of all known substances in the organic kingdom. Without it no life appears possible on our planet. The name protein comes from a Greek word meaning "to take first place."

There are about twenty amino acids. Each one is made of carbon, oxygen, and hydrogen, with the added bonus of nitrogen which makes protein different from the carbohydrates and fat. Like the twenty-six letters of the alphabet, which can be combined to form many different words of numerous letters, the amino acids can be combined in specific sequences to form protein molecules containing thousands of amino acids. And protein still takes first place, nutritionwise. Supplying adequate protein to the people, especially the children, of the world is the major nutritional problem today and is of international concern. Efforts to find a solution involve not only nutritionists, biochemists, and food technologists but statesmen also.But protein is needed not only in other lands; it is essential to you and your family, your health and vitality. Since all living substances contain protein, it is necessary for life—your life. Why is protein so important? What does it do in the body and for the body?

It is a protein—haemoglobin in the red blood cells—which carries oxygen from the lungs to the tissues and carbon dioxide from the tissues to the lungs. It is proteins—albumin and globulins—which are involved in the exchange of water and minerals between the blood, lymph, and tissues. If the protein level in the serum decreases, the fluid balance becomes upset, water accumulates, and oedema results.

It is proteins—enzymes and most hormones— which effect metabolism. It is proteins—gamma globulins —which as antibodies can destroy bacteria viruses, and other microorganisms in the body and sometimes confer temporary or permanent immunity to specific diseases. Proteins also serve as buffers in the complex system which keeps the blood in a slightly alkaline condition.

To grow, a child needs ample protein, and the need does not stop when he grows from youth to adulthood. Throughout life proteins in all living tiof this the daily diet should supply adequate amounts of protein even after the growing years are over. One gramme of protein furnishes four calories. Since your body's need for energy must be met, proteins will be used if carbohydrates and fats are low in the diet. Carbohydrates are sometimes called protein sparers because they supply fuel and energy and spare protein for its other important functions. Plants are able with the help of the sun to make their own protein from carbon dioxide, water, and the nitrogen in the air and soil; but human beings and animals must get their protein from plants or from other animals. The proteins of each plant and animal species differ from every other. Proteins in various parts of the body differ—muscle, skin, and haemoglobin protein are not the same.

Each protein is a large and complex puzzle, usually containing thousands of amino acids joined in a specific sequence. If this sequence is broken by one amino acid missing or out of place, the results may be serious. For example, in the cases of persons suffering from sickle cell anaemia (when a specific amino acid is replaced by a different one) the life span is shortened.

To be absorbed from the digestive tract, protein has to be broken down by digestive enzymes into the original amino acids, If a large molecule of protein were to be taken directly into the blood without being broken down into amino acids, allergic reactions would occur. Thus complete proteins replenish the body's amino acid pool. The muscles contain one third of your total body protein, the skin contains one fifth, and- various other parts of your body contain the remainder of your total proteins.

The terms "essential" and "nonessential" are sometimes used to characterize amino acids. Your body can synthesize some amino acids but others it cannot. Those which cannot be synthesized are called essential amino acids and must be present in the food. They are leucine, isoleucine, lysine, methionine, phenylalanine, threonine, tryptophan, valine (and also histidine for children). The so-called nonessential amino acids can be manu-ssues factured by your body from other nutrients or from the essential amino acids.

Probably you have heard about complete, partially complete, and incomplete proteins. Such terms refer to the amoiunt and proportion of essential amino acids present in a protein. Complete proteins have all the essential amino acids in sufficient amounts and proportions to support growth and maintain life, even when they are the only protein in the diet.

Partially complete proteins have all of the essential amino acids but in inadequate amounts or incorrect proportions. 'When they are the only protein in the diet they will sustain life but not growth. Incomplete proteins lack one or more of the essential amino acids and will neither support growth nor maintain life.It is seldom that only one protein is used in a meal; therefore the classification of complete or incomplete usually affects only those individuals with limited food available or those on dietaries used for experimentation.

Foods from animal sources such as milk, cheese, eggs, meat, fish, and poultry contain complete proteins and thus supply all of the essential amino acids. Soy-bean, garbanzo, and peanut proteins have been compared with animal protein in quality. Green leafy vegetables also furnish excellent protein but in such minute amounts that they do not contribute much to the protein requirements.

Proteins in grains, nuts, most legumes, vegetables, and fruits are frequently classified as partially complete. Fortunately proteins of different foods can supnlement each other. A meal which combines two or more foods with partiallv complete or incomplete proteins may provide protein of good quality which will support life and promote growth.

Good amino acid balance can be obtained by combining cereals with legumes, nuts, milk, cheese, or eggs. Throughout the ages people have practised supplementation of protein instinctively. Many cereal proteins are low in the amino acid lysine, but fairly well-supplied with sulphur-containing amino acids. Thus legumes and cereals may supplement each other. One study found that a combination of beans and rice resulted in a nutritive value similar to that of a complete protein. Some legumes and nuts may supplement each other and are good sources of minerals and vitamins as well.

Digestibility of protein bears on its nutritive value. Your cooking methods also affect the value you receive from the proteins in your food. Some of the amino acids, such as lysine, are unstable and may be destroyed bv overheating, toasting, or frying. However, cooking in water improves the digestibility of beans and wheat proteins.

Since every protein contains nitrogen, the protein needs of people and animals have been investigated by nitrogen balance studies. These studies are customarily carried on for a number of days or weeks in order to determine the variations from day to day. There are two considerations in nitrogen balance studies: first, the intake of protein in the food; and, second, the output of nitrogen in the body excretions. The intake of protein is determined by chemical analysis of the foods or by calculating from tables of nutritive values. The output of nitrogen is ascertained by laboratory tests.

When nitrogen in the food is more than the amount excreted by the body, you are in positive nitrogen balance. When the intake equals the excretion, there is nitrogen equilibrium. In contrast, if the nitrogen intake is less than the output you are in negative nitrogen balance.

A normal adult should be in nitrogen equilibrium. During growth, pregnancy, and lactation, the need for protein is increased. New tissues are being built and nitrogen is retained. In other words, there should be positive nitrogen balance.

In wasting disease, burns, starvation, and fevers, there is much tissue breakdown. If the supply of protein in the diet is low at such times the body will draw from its own tissues to supply the lack and there will be a negative nitrogen balance.

Protein Sources

. Protein of good quality can be obtained from both animal and plant sources.Milk and milk products, eggs, meat, poultry, and fish are protein foods of animal origin.

Plant proteins

are contained in legumes (beans,peas, lentils, garbanzos, and peanuts), nuts (such as walnuts, pecans, cashews, almonds), and cereals (wheat, rye, oats, corn, rice, barley, millet). Vegetables and fruits contribute only a small portion of protein. Seeds of sesame, cotton, sunflower, pumpkin, and squash have relatively high percentage of protein.Some spun soybean products and vegetable protein manufactured from legumes, nuts, cereals, wheat glutten, and soybeans approach the taste and texture of meat. These products make inexpensive main dishes which are both nutritious and tasty.

Plant protein sources, if properly chosen and combined, can meet the needs for the essential amino acids and contribute to an adequate diet.

Protein Requirement

. Karl von Voit, a German physiologist and nutritionist, established the first protein requirements in 1881. He believed that people needed 118 grammes of protein daily to sustain good nutrition. He based his conclusions on surveys of German workers in Berlin.

Later at Yale University, Russell H. Chittenden, who was the first physiological chemistry teacher in America, questioned von Voit's Standards. He experimented on himself and others, including young athletes, during periods of six months to more than a year and found that diets containing only 53 grammes ofprotein a day could maintain proper balance.

In 1920 Henry C. Sherman of Columbia University analyzed all of the available evidence on protein requirements. He came to the conclusion that one half gramme of protein daily per kilogramme (2.2 pounds equals one kilogramme) of body weight was sufficient to meet the body's needs. Further experiments have shown that even less protein is sufficient if the protein quality is good. Dr. Sherman, however, advised a fifty per cent mark-up from the one half gramme as a "margin of safety."

Nutrition experts provide a safety margin and suggest 0.9 grammes per kilogramme of body weight. This means 65 grammes protein each day for a normal healthy adult man weighing about 154 pounds (70 kilogrammes). During pregnancy 65 grammes are recommended and 75 during lactation. The amounts for children vary with size and age.

Protein Deficiency.

In areas where dietary protein is poor in quality or scarce, malnutrition especially during infancy and childhood is common. Protein deficiency is particularly prevalent in the low socio-economic brackets among infants and children, pregnant and nursing women, and elderly people.

Malnutrition

Malnutrition may occur when there is a low protein intake due to lack of knowledge or misinformation regarding protein needs; when fasting or dieting without medical advice; or when excessive loss of protein takes place as with haemorrhage, burns, fevers, wounds, and starvation.

Kwashiorkor

Kwashiorkor, a widespread pronounced form of malnutrition, results largely from protein deficiency. The condition is known as shibi gachaki in Japan, mehlnuhrshaden in Germany, male de farina in Italy, and sindrome pluricarencial infant!) in Central America. Economic, social, sanitary, and educational factors contribute to its high incidence.

It occurs most often in infants after weaning, when the diet which replaces the mother's milk is very deficient in protein and consists largely of carbohydrates. Among the symptoms are malnutrition, oedema, lesions of the skin resembling pellagra, apathy, loss of appetite, diarrhoea, poor resistance to infection, retarded growth, and discolouration of the hair.

The treatment of kwashiorkor includes administering protein of high nutritive value. When reconstituted non-fat milk was fed to a group of children with kwashiorkor, thev made dramatic improvement. A good diet with all the essential nutrients from available local food is given as soon as tolerated. Supplementation of the diet in the weaning and postweaning periods contributes most to preventing kwashiorkor.

Vegetable proteins are being studied in the laboratories of many countries in their efforts to find a solution to the world's protein problem.