Food and You
Dallas E. Boggs, PhD
The Composition of Food
WHAT IS FOOD? The answer to this question seems obvious—it is whatever man eats and drinks. However, merely knowing the names of different foods will not satisfy the curious person—he will want to know what the chemist finds when he takes a food apart and also something about the many fascinating chemical reactions that enable the body to transform meat, potatoes and bread into blood, bone and muscle. The science of chemistry makes it possible to define food and its functions in precise terms. Chemical analysis reveals that nearly all foods, as they occur in nature, are composed of proteins, fats, carbohydrates, vitamins, mineral salts and water. These substances are sometimes referred to as the foodstuffs.
Many natural foods are processed for one reason or another, and the end product may consist mainly of only one of the foodstuffs. For example: Casein, derived from milk, is a protein; granulated sugar is pure carbohydrate; and margarine is mostly fat. Certain dietary deficiency diseases may appear when too much highly refined food is eaten over long periods of time. It is quite feasible to eat enough of such a diet to satisfy the need for calories, but it is likely to be deficient in some of the essential nutrients. In the milling of white flour, for example, the germ and outer covering of the wheat kernel are discarded; but these are the very portions of the grain that are richest in vitamins and minerals as well as the fiber that facilitates the transport of waste products through the digestive system.
Protein is a term that comes from the Greek and means "of primary importance". It is impossible to survive long without protein. Furthermore, life would scarcely be worth living without the foods that contain generous amounts of this foodstuff. The best sources of it are meats of all kinds, milk, eggs, whole cereal grains, peas and beans—imagine a diet without any of these foods!
Many kinds of proteins are found in nature; but they all have one peculiarity in common; that is, they are composed of about I6% nitrogen. In the gaseous state, this same element makes up about 79% of the air we breathe. Unfortunately the body cannot use a single atom of the nitrogen in the air but must get this important element from dietary proteins.
All proteins consist of very large molecules that are built up with various combinations of smaller building blocks called amino acids. More than 20 different amino acids are known, and each one contains at least one atom of nitrogen per molecule—in a form that can be utilized in the body. Ten of the amino acids have certain peculiarities in their structures that make it impossible for the animal body to synthesize them from simpler substances. These are, therefore, referred to as the essential amino acids and must be supplied ready‑made in the food.
Plants, on the other hand, are generally capable of manufacturing all of the amino acids from relatively simple substances—namely, the carbon dioxide of the air and the nitrogen and water of the soil. This is just one instance of the complete dependence of animal life upon the plant kingdom; but this fact is not to be taken as unqualified support for the vegetarian's point of view. It happens that the plant proteins are not exactly suited to the needs of man; a few of the essential amino acids may be present in too small amounts for best human use—in some plants they are either absent or present only in traces. For instance zein, the protein of corn (maize), is almost devoid of two of the essential amino acids. We known, as the result of feeding experiments, that an animal cannot grow nor even maintain its weight if the sole source of dietary protein is corn. However, corn is not condemned as a food on this account. In order to get the most out of corn, the obvious practice is to arrange the diet so that the deficiency is made up by including some other protein. Milk, for example, contains an abundance of the amino acids that are lacking in corn. To make the required adjustments, it is not necessary to be a chemist; a good practical rule is to include a considerable variety of foods in each meal. The chances are good that in a mixture of foods the amino acid deficiencies of one protein will be corrected by the presence of others not short of the same amino acids.
That the body utilizes some proteins very well and others very poorly suggested that the proteins should be classified according to their usefulness. The result is a scale of "biological values". If a certain protein can be utilized completely, it may be considered to have a biological value of 100%; if the amino acids are only half utilized, the biological value is 50%. This quality of a protein is limited by a relative scarcity of one of the essential amino acids. The protein manufacturing machinery of the body is highly specialized and operates only under certain conditions. For maximum efficiency, all of the essential amino acids must be present simultaneously in exactly the right proportions. If one of them is present in less than the ideal relationship to the others, wastage occurs; and the biological value of the mixture is reduced. If one of the essential amino acids is entirely missing, the body may not be able to make any new protein. This process operates on an "all or nothing" principle—it either works in a specified way or not at all.
As the result of many experiments on man as well as the lower animals, it is generally agreed that the proteins of whole egg stand at the head of the list with a biological value of 95 to 100%. The proteins of other common foods are arranged in the scale approximately as follows: milk 85%, meats 75%, rolled oats and whole wheat 65%, corn 50%, wheat gluten 40% and gelatin 25%. Excepting gelatin, the proteins of animal origin are better utilized than those that come from plants. It makes good sense that the egg should head the list because it is capable of furnishing everything required for the development of a new individual.
Meats, milk, seeds and nuts are all natural sources of fat. Chemically, fats are simpler than the proteins because they are composed of carbon, hydrogen and oxygen, and do not contain nitrogen. The molecule of fat is composed of glycerin combined with fatty acids, and they do not form such huge molecules as the proteins. Both plants and animals are able to manufacture fats from other substances, especially the carbohydrates. Every farmer knows that a pig can convert large quantities of starch into fat. A great many humans have discovered (to their consternation!) that they also have this ability in common with the pig.
Certain "unsaturated" fatty acids must be supplied as such in the food. They are called unsaturated because there is not enough hydrogen in the molecule to saturate all of the carbon atoms. Thus, there are essential fatty acids as well as essential amino acids, and man must acquire them preformed in his food. This is one more reason for including a large variety of foods in the daily dietary. Several foods contain unsaturated fatty acids; but they are especially abundant in nuts and in corn, olive, linseed and fish oils.
One of the most important purposes of fat is for storage of food energy. Calories not used for current needs are put away in the form of fat against the time when food may not be available. In starvation or undernutrition, these stores supply most of the calories required to keep the body alive. A gram of fat contains more than twice as much energy as a gram of either protein or carbohydrate. The brain and nerves contain considerable amounts of fatty material; it seems to be part of the structure of these tissues. Fats are important in maintaining the health of the skin, and they have much to do with making the body covering almost impervious to water. Finally, fat, as a component of foods, has what dietitians call "satiety value"; this means that, for equal bulk, the meal that contains the greater amount of fat will give the greater feeling of satisfaction. Fats are also important for transport and storage of the fat soluble vitamins.
Carbohydrates are the cheapest and most abundant of foodstuffs. They are represented in nature by the celluloses (fiber), starches and sugars; and all are made up of only carbon, hydrogen and oxygen. No single carbohydrate appears to be essential for the body in the sense that it must be supplied prefabricated in the food. The body seems to prefer glucose for its various metabolic processes; but is quite capable of making this sugar—not only from other carbohydrates but also from proteins. The energy needed by the body is much more efficiently released when carbohydrate is present. When mostly fat is being burned, as in starvation, it may be thought of as burning with a "smoky flame". A little carbohydrate is a great help in clearing up the smoky flame of burning fat; and, of course, carbohydrate burns very well all by itself. It is the preferred fuel of the muscles and, normally, the only fuel of the brain.
The following facts apply to all vitamins: (1) They are absolutely essential for health; (2) they must be supplied as such in the food because the human body is unable to synthesize them; and, (3) the amount required each day is very small. They fall into two categories--based on solubility. Vitamins A, D, E and K belong in the "fat soluble" group; they are associated with the fats and are soluble in them as well as in fat solvents such as ether and alcohol. All of the other vitamins are lumped together as the "water soluble" group.
The term vitamin is constructed from the two words "vital" and "amine." They were used by an early biochemist to describe a substance ("vitamine") that was vital to health and thought to belong to the class of organic compounds known as amines. Since that time (1912) many vitamins have been discovered; and, chemically, they are a heterogeneous lot. All of them are vital for health, but most of them are not amines; hence, it was agreed to drop the final e to give “vitamin”.
The vitamin content of foods is quite variable, depending upon place of origin, kind of plant or animal, means of transportation, handling and processing. A plant source can begin its journey to the table with very respectable vitamin content and lose some of it in passing the hazards mentioned above. It is a matter of concern that every precaution should be taken to preserve the vitamins that nature has placed in the food plants; and, with proper care, it is possible for the normal individual to obtain all of his vitamin requirements solely through his diet. Sometimes a physician may prescribe pills for added insurance (such as for women during pregnancy), but for the healthy individual to indulge in indiscriminate guzzling of vitamin preparations is usually a waste of money and material.
This category includes a great many chemical elements combined in various ways. The combination of sodium and chlorine to form table salt is the familiar example. Sodium chloride is about the only mineral salt ever seen by most people. The other elements are combined with various foodstuffs—and in such small amounts that they are not recognizable on casual inspection. Calcium and phosphorus, which are so important for the building and maintenance of bone, are present in milk but can be identified only by means of chemical analysis. Iron, so important for making new blood, is present in very small amounts in many foods. The liver, heart and muscle of beef, and eggs are good sources of iron; while milk is very deficient in this element. Iodine is extremely important in the vital economy, but the amount required daily is incredibly small. Despite this fact some regions are lacking in iodine; and, in the past, this deficiency often manifested itself by a high incidence of goiter. Manufactorers now include sodium iodide in our table salt to correct such deficiencies. Fish and other foods gathered from the sea are excellent sources of iodine.
The mineral elements mentioned in the previous paragraph often are not present in adequate amounts in the diet. Before processing, most foods contain little sodium chloride and hence the salt is commonly is added to them, but the amount added is usually based more on taste preferences than on nutritional quality. Children who live too long on an exclusive milk diet are likely to develop anemia because of a low intake of iron. On the other hand, children who get little or no milk in their diet will probably not have enough calcium and phosphorus to develop good bones and teeth.
A number of elements are usually present in sufficient amounts in the average diet. Among these are potassium, magnesium, manganese, cobalt, zinc, sulfur and several others. There is great interest in fluorine, especially as it affects the decay of teeth. The incidence of dental caries is very low in regions where the water contains an appreciable amount of that element. This parallelism is so striking that cities and states now add it to their public water supplies to improve dental health.
Other Substances in Food
When the body uses oxygen or breaks down certain fats or proteins as a normal part of metabolism, it gives rise to substances called free radicals. Environmental factors like cigarette smoke, exhaust fumes, radiation, excessive sunlight, certain drugs, and stress can increase free radical production. A free radical is a chemically unstable molecule that is missing an electron; it will react with any molecule it encounters from which it can take an electron. In their search for electrons, free radicals react with fats, proteins, and DNA, damaging cell membranes and mutating genes. Because of this, free radicals have been implicated in aging, cancer, cardiovascular disease, and other degenerative diseases like arthritis.
Antioxidants can help protect the body from damage by free radicals--in several ways. Some dietary antioxidants prevent or reduce the formation of free radicals; others remove free radicals from the body by reacting with them directly--donating electrons. Antioxidants can also repair some types of free radical damage after it occurs. Some antioxidants, such as vitamin C, vitamin E, and selenium, are also essential nutrients; others, such as carotenoids found in yellow, orange, and deep‑green vegetables, are not. Obtaining a regular intake of these substances is vital for maintaining the health of the body. Many fruits and vegetables are rich in antioxidants.
Some phytochemicals (found in plants) are antioxidants that may help prevent some of the chronic diseases. For example, certain substances in soy foods may help lower cholesterol levels. Sulforaphane, a compound isolated from broccoli and other cruciferous vegetables, may render some carcinogenic compounds harmless. Allyl sulfides (a group of chemicals found in garlic and onions) appear to boost the activity of cancer fighting immune cells. Further research on phytochemicals may extend the role of nutrition to the prevention and treatment of many chronic diseases. Like many vitamins and minerals, isolated phytochemicals may be harmful if taken in high doses. In addition, it is likely that their health benefits are the result of chemical substances working in combination. It is best to obtain them by eating a variety of fruits, vegetables, and grains rather than relying on supplements. This is especially true for anyone taking prescription drugs, which often interact with herbal supplements.
Effects of Food Processing
Food processing includes all steps taken to prepare it for human consumption—from harvesting the plant or slaughtering the animal to the cooking of food served at the table. All plant and animal tissues begin to deteriorate after harvesting—due to the action of enzymes contained in them and to invasion by bacteria from the outside. Animal tissues, in particular, decompose very rapidly unless they are kept chilled or frozen.
Some plant products resist deterioration—hard wheat, for example, can be stored for years. Many of the vegetables, on the other hand, do not stay fresh very long; like meat, they must be kept chilled. Frozen foods retain almost all of their nutritive value for one year or longer.
The changes that take place in stored food are not all as evident as the wilting and discoloration of lettuce. There may be a large decrease in vitamin content that cannot be detected except by chemical analysis. Riboflavin, one of the vitamins in milk, is rapidly destroyed by the action of light; the ascorbic acid (Vitamin C) in orange juice is readily oxidized by air. Thus, milk should be kept in the dark, as well as in the cold, and orange juice should be frozen when not used promptly after extraction from the fruit. In general, it is desirable to keep all fresh foods at low temperature, in the dark, and in closed containers so that the exposure to air is minimized.
Most food processing requires concession between maximum retention of nutritive value and prevention of spoilage. In heat sterilization, for instance, the high temperature tends to destroy vitamins and reduce the biological value of proteins. It is desirable to reduce the time and intensity of heating to the minimum required to stop enzyme action and to kill harmful bacteria. Heating beyond this point is a waste of both food and fuel. The pasteurization of milk illustrates a compromise in food preservation; the short, moderate heating kills pathogenic bacteria, but it tends to reduce the nutritive value of milk. It is sensible to take this small nutritive loss in pasteurized milk in order to have a product that is safe for human use. Industry, on the whole, has made remarkable progress in retaining the nutritive values of canned foods; their vitamin content is very nearly the same as the fresh product.
It is common practice in the processing of cereal grains for human consumption to refine them to a high degree. In the milling of wheat for flour, the outer portion of the kernel is removed—and with it goes a large portion of the vitamins and minerals and the fiber. This material is fed to hogs and cattle with obvious benefit to them; but man has been content to eat what remains. White flour usually represents less than three fourths of the whole wheat. Most white flours are bleached with agene, a chlorine compound; according to some experiments in dog feeding, agene seems to damage the wheat proteins. But, it must not be concluded that everybody should return to the use of whole wheat flour; many people are unable to tolerate the roughage found in whole wheat products. It may reasonably be concluded, however, that modern milling practices have carried flour refinement too far and that there might be a compromise that would contribute significantly to the health of the nation. This need was recognized during World War II, and the "enrichment" of white flour was instituted. Enrichment in this sense means simply adding a few synthetic vitamins and some iron to ordinary white flour. Wheat is milled and refined until it is deprived of much of its food value; then, chemists synthesize vitamins that are subsequently mixed with white flour to make a partial restoration. On the face of it, this appears to be a rather awkward solution to a problem of national concern.
Some of the prepared breakfast foods are subjected to excessive heat treatment, and this results in appreciable damage to their proteins. Since many of the vitamins also are destroyed by heat, it is probable that some of the products retain only a small fraction of their original nutritive value.
Although the science of nutrition is growing steadily, it cannot be emphasized too strongly that large areas of this field of investigation remain unexplored. Scientifically controlled feeding of domestic animals has received more attention than the nutrition of man. One of the reasons for this state of affairs is that efficiently fed cows and pigs are profitable in terms of money; the profit to be derived from a well‑nourished man cannot be expressed in the same terms. Another reason for the lag in studies of human nutrition is the reluctance of scientists to experiment on man without preliminary animal tests. The results of animal investigations are extremely useful in planning experiments on man; and thus gross errors have been avoided. This fact is sufficient justification for the use of animals in nutrition research; but it should be recognized that different animal species have somewhat different food requirements. The final word on the food needs of the human being must come from research in which man himself is the experimental animal.
Cooking should interest everybody in one way or another. Many foods are not palatable unless properly cooked, and the art of cooking is an old and honorable one. Besides increasing palatability, cooking kills harmful bacteria and softens and breaks up cellulose fibers—a process that may be considered the first step in digestion. There are other less obvious benefits of cooking. For example, soy beans contain a substance that interferes with their own digestion; when the beans are heated, the interfering substance is destroyed.
Some fishes contain an enzyme that destroys thiamine, one of the B vitamins; cooking completely inactivates the undesirable material. The presence of this peculiar enzyme was first discovered in feeding foxes a diet that contained raw fish. The animals gradually developed a type of paralysis that is characteristic of thiamine deficiency. The individual components of the diet were known to contain adequate amounts of the various vitamins; but when they were mixed together for feeding, thiamine was destroyed. After much research, it was discovered that something in the raw fish combined firmly with the thiamine of the diet—thus depriving the foxes of this important vitamin. At first sight this fact seems totally unrelated to the feeding of civilized man because he does not eat raw fish; but clams, which are often eaten raw, are especially active in combining with thiamine. Raw oysters, on the other hand, do not have this undesirable property. Raw egg white contains a substance that combines with biotin, another of the B vitamins; and here again heat is effective in destroying the offending material. It is evident from these few examples that many unseen benefits are derived from the cooking of food.
It should not be assumed, however, that all types of cooking are beneficial. Foods are often overcooked with the result that much of their flavor is lost and some of the vitamins are destroyed. Another common fault in cooking is the use of too much water. The cooking water is usually discarded, and with it goes a large share of the vitamins and mineral salts that were present in the raw food. This practice led someone to remark that the kitchen sink is the best nourished member of the American family.
Some cooks add baking soda to spinach or other green vegetables to preserve the bright color, but this practice causes destruction of vitamin C at a very rapid rate. These few examples of malpractice in food preparation indicate that the cook, through ignorance or prejudice, can ruin the best of foods. It is difficult to convince many people of these facts because the changes that occur are not usually detected by the senses of sight, smell or taste. A vegetable that has had its vitamins destroyed by improper cooking may taste and look like one that has been properly cooked. It is only by using the special methods of the analytical chemistry that it is possible to prove just what has gone wrong.
Since food is so important in the daily life of every citizen, it seems sensible that he should be reasonably well informed on the subject. An enlightened public opinion can do much to determine whether food shall be offered to the public on the strength of an advertising slogan or on the basis of nutritive value.