The people of the nation are becoming more and more nutrition conscious. This trend appeared before the war, but the movement for better nutrition has been accelerated by the presence of our fighting.men in far-flung arctic and tropical regions, and all that this entails. No apology is made for selecting the age-old problem of protein as the nutrition problem to be discussed here, for the question is stilt being asked, "Where shall I get my protein?"
The pendulum of emphasis in any field tends to swing with current research. At one time the slogan in nutrition was "Count the Calories";then, with the discovery of the importance of little things in the diet, the clarion call became "Value the Vitamin," until today the American people are buying vitamin pills to the tune of more than $150,000,000 a year. But it should be remembered that good nutrition cannot be achieved by adding a vitamin tablet to an adequate diet poorly prepared.
Protein was among the first of the food elements to be studied. Its importance was recognized from the beginning, for the name itself is taken from the Greek, meaning "to take first place." The proteins have never received the glamour that some of the other nutritional factors have enjoyed, because the study of them has been slow and tedious. With the recent rationing of meats they probably reached as near headline proportions as they ever will. However, sound nutrition thinkers have always given them an important place in the diet.
The protein molecule is very complex, being made by the linkage of structural units called amino acids. Upon digestion, proteins yield twenty to twenty-five different amino acids. The differences between proteins are largely number, kind, and arrangement of these acids within the protein molecule. Since the protein molecule is made up of hundreds and even thousands of amino acids, full understanding of their structure is difficult. This accounts for the slow progress in the study of these compounds.
Proteins are the chemical base of all living cells and tissues. They also enter into the structure of enzymes, hormones, red blood cells, and body fluids. Without proteins life cannot go on. There is accumulating evidence that an adequate quantity of dietary protein is essential for normal hemoglobin formation. There are reports which correlate an inadequate protein intake with the incidence of macrocytic anemia. Recently it has been found that large amounts of the amino acid, alanine, can completely replace the B vitamin, pyridoxine, as a growth factor for the microorganism,
Streptoccoccus lactis R. Since a part of the pyridoxine molecule is actually made up of alanine, this amino acid might be a precursor of pyridoxine. Present studies on amino acids may add to a fuller understanding of certain deficiency diseases.
According to Rose, eight of the amino acids are essential for the growth and body maintenance of man. Some proteins do not contain all the essential amino acids and are therefore said to be "incomplete proteins." Foods containing incomplete proteins should be augmented by those containing complete proteins. The low biologic value of certain proteins, such as those from certain vegetable sources, can be considerably enhanced by the inclusion of proteins of animal origin in small amounts. For example, Swaminathan raised the nutritive value of rice very materially by the addition of relatively small amounts of skimmed milk. A mixture of two incomplete proteins will often be of greater value to the body than either taken alone. For this reason it is best to obtain our protein supply from more than one source. In view of this it will be seen that it is not enough to inquire, "Where is the protein?" But one must also ask, "What is the quality of the protein?"
For those not using meats, the best sources of complete proteins are milk, cheese, eggs, soybeans, and peanuts. Incomplete proteins are found in dried peas, beans, lentils. Although cereals are not classed as high-protein foods, yet it is true that cereal grains are the largest single contributors of protein to the national dietary. More than one third of the protein in the ordinary mixed diet is derived from this source. Cereal proteins provide a somewhat less satisfactory amino acid mixture than do animal proteins, but there is ample evidence to prove that these deficiencies are adequately supplemented by proteins from milk, eggs, and so forth, in the rest of the diet. Nuts are a valuable supply for protein, and the proteins of some of the nuts are complete.
What Certain Foods Have to Offer
Milk, along with eggs, stands at the head of the list so far as availability of proteins is concerned. In addition to supplying complete proteins of high quality, it offers a dependable source of calcium. The phosphorus content is high and it supplies riboflavin and some thiamin. Whole milk is a good source of vitamin A.
Cheese is really concentrated milk, therefore one would expect to find the same elements as in milk. Cottage cheese and the cream cheeses are the most healthful types.
Eggs contain proteins that are complete and of high nutritive value. Eggs are rich in a number of the vitamins, especially vitamins A and D. They are also sources of three important minerals —calcium, phosphorus, and iron.
Nuts are excellent for growth. Their offerings vary with the type of nut. Brazil nuts, cashews, almonds, pecans, and coconuts have been found to be adequate for growth. Chemical analysis of individual proteins from some of these have shown an amino acid assortment rather similar to that of meat. Almonds are rich in calcium, phosphorus, iron, and thiamin ; pecans supply only small amounts of calcium and iron, but are a good source of phosphorus and thiamin. Walnuts are a very good source of phosphorus and thiamin. Peanuts are an excellent source of complete protein, phosphorus, thiamin, and riboflavin, and contain some iron.
Cereals are important sources of protein even though they do not have quite the growth-promoting value that the proteins of milk and eggs have. Combining cereals gives an amino acid mixture that is of greater use to the body than single grains. The proteins of wheat embryo are as good as milk. It is not surprising, then, to find that whole wheat supports growth better than refined-wheat. Oats are higher in protein than most cereals, and the quality of the protein is relatively high. It has been found that processing by means of the explosion technique causes considerable damage to the protein quality of oat products. Flaked and inflated whole wheats also rank quite low in value. This is presumably the result of the high heat treatment involved. Whole wheat is a very good source of iron and phosphorus. It also furnishes thiamin, riboflavin, and niacin.
Legumes contain proteins that are rated low in value mainly because of an inadequate amount of the sulphur-containing amino acids. The Alaska field pea is an excellent source of the amino acids essential for growth, with the exception of methionine. The nutritive value of legume proteins is improved with cooking. In addition to their richness in starch and protein, this group of vegetables is characterized by being very high in iron, phosphorus, and thiamin, and they also contain a fair amount of calcium.
Soybeans are an exception to the rule that legume proteins are incomplete. Soybean protein has almost the same quality as that in meat, eggs, milk, and cheese. Jeanette B. McCay, representing the New York State Emergency Food commission, states : "Soys offer the greatest hope for feeding a hungry, war-weary world. Probably they contain the highest nutritive value in the smallest space, and the highest nutritive value for the least money and the least labor in production of any natural food." Besides protein, soybeans provide B vitamins, particularly thiamin, riboflavin, and niacin; and three minerals—iron, calcium, phosphorus. The sprouted beans are rich in vitamin C. The niacin and riboflavin content increase in the sprouting process. Finally the soybeans are so versatile that they may appear in any part of our menus from soup to nuts.