Food and You
Dallas E. Boggs, PhD
Foodstuff Requirements of Man
THE BODY continuously loses heat from the skin—hence, the need for periodic refueling (at mealtimes). Offhand, it would appear that a man who weighs twice as much as another should require twice as many calories; but heat loss is determined by body surface area rather than weight. According to "The Law of Surface Area", a man 173 centimeters (5 ft. 8 in.) tall and weighing 120 kilograms (264 lbs.) requires only 35% more calories than a man of the same height but only half the weight. (The body surface of the heavy man is 2.3 square meters and of the light one I.7 square meters.) In order to maintain a constant temperature, the body must produce as much heat as it loses to the surroundings. The minimum heat production is called the basal metabolism.
The calorie is a measurement of energy—the amount of heat required to raise the temperature of one kilogram of water one degree Centigrade (large calorie). To say that a portion of food contains a certain number of calories means simply that if it were burned it would yield so much heat. Protein, fat and carbohydrate are burned in the tissues and yield their calories to the body, which uses the energy to keep warm and to power the muscles and organs. The foodstuff burns in the body without flame, but the presence of oxygen is necessary and the end products (carbon dioxide and water) are the same as in the burning of wood, coal or oil. The proteins do not burn completely, and the result is that portions of the their molecules are excreted in the urine as urea and amino acids.
Several factors can increase the metabolism or heat production. Most important among these are cold, muscular exercise and food. When the temperature falls, more heat is lost from the skin, and the body compensates by stoking up the fire—the stored fat and carbohydrate are burned at a greater rate in order to provide the extra calories. Also, more fat and carbohydrate are burned when muscles are exercised. When muscular work is expressed in calories, the body produces four calories of heat for each calorie of muscular work accomplished. In other words, of the total of five calories delivered by the muscle as work and heat only one appears as work, and the remainder as heat—an efficiency of 20%. This explains why exercise is so effective in "warming up" on a cold day. Heat production is also increased when food is being digested and absorbed, and this effect is most marked after a meal that contains much protein. The warm feeling that follows a big steak dinner is due in part to the increase in heat production caused by the digestion of proteins.
The caloric needs of the body of normal individuals are met by satisfying the demands of hunger. The physiological mechanisms of hunger are not well understood, but most people have experienced it as either a series of sharp pains or a general vague feeling of emptiness in the abdomen. The sensation is due (in part at least) to severe muscular contractions or cramps of the empty stomach (hunger pains). Recent identification of two hormones may lead to better understanding of appetite. Ghrelin, produced in the lining of the stomach, appears to signal to the brain when the stomach is empty—and thus stimulates appetite. Leptin, made by fat cells, appears to be an appetite suppressant. Eating in excess usually means satisfying the appetite for certain foods such as desserts, and this loads the body with more calories than it needs. The only possible outcome of such practice is that the extra calories are stored as fat.
It is important to distinguish between hunger and appetite. Hunger is the sensation of emptiness that develops when the body runs low on fuel; whereas, appetite is acquired by experience. Thus a man may be ravenously hungry but have no appetite for spinach, or he may be completely stuffed with ordinary fare but still have an appetite for ice cream. When appetite gains the upper hand, the spare tire around the midriff is assured. If a conscious effort must be made to maintain a normal body weight, it is much more sensible to guard the appetite than to try to work off fat that has already been deposited. (A pound of fat will yield enough calories for a day of very strenuous work.) One of the natural consequences of strenuous work is an increased sensation of hunger, which in turn induces a greater intake of food. But there is evidence that vigorous exercise can moderate the vicious circle of weight gain and loss that leads to obesity.
The average man needs about 75 calories per hour to meet the demands of his basal metabolism, making a total of 1800 calories for 24 hours. If he does light work in an office or laboratory for eight hours and putters around home for another eight hours, he will need an additional 75 calories per hour for the 16 hours he is awake. If this extra amount of 1200 calories is added to the basal, the total for the 24 hours is 3000 calories. If, on the other hand, the man should be a lumberjack working outdoors in cold weather, he might easily require 300 calories per hour for his eight‑hour shift, making his total requirement 4800 calories per day.
The following table gives the caloric value of average portions of a few common foods:
Food Average Portion Calories
Bacon 4 slices 28 grams 145
Beefsteak ¼ lb. 113 “ 265
Halibut ¼ lb. 113 ” 135
Eggs l 50 “ 80
Milk, whole I glass 210 " 150
Cheese I oz. 28 " 110
Butter 2 pats 12 " 100
Bread 2 slices 50 “ 130
Potato I medium 120 “ 100
Carrot I large 100 “ 40
Beans, green I cup 100 “ 35
Apple l 150 " 90
Orange Juice 1/2 cup 100 “ 50
Olives 5 25 " 35
Sugar 2 teaspoons 8 “ 30
Oil (Salad) 1 tablespoon 11 “ 100
(I ounce is approximately 28 grams)
From these data, it is evident that the most appetizing foods (meats, eggs and dairy products) are those that supply the most calories per portion. Many people attempt to reduce their weight by omitting certain items of the diet; and butter, bread and potatoes are often singled out for this purpose. Actually, a medium sized potato contains less than half the calories found in an average serving of beefsteak, and a slice of bread contributes fewer calories than an egg. It is hazardous, however, to devise a reducing diet based solely on its calorie content.
First, the reducing diet must supply enough of the different nutrients needed to maintain the body in health. This end is best achieved by eating a varied diet. Cutting out certain items such as butter, bread and potatoes, could very well result in a deficient diet. It is much safer, and usually easier, to reduce the daily intake of all portions of the menu. If single items must be omitted, perhaps the omission of desserts and midnight snacks may be innocuous.
(Click on web.md to view some current weight loss diets.)
The Protein Requirement
Protein is an essential component of the body structure. The muscles, skin and internal organs are approximately one quarter protein and three quarters water, and even the bones contain some protein. The body, like a machine, is subject to wear; but, unlike a machine, it can repair itself when the diet is adequate. It will be recalled from the first chapter that proteins contain about 16% of nitrogen. This fact is utilized in estimating how much protein is present in the diet as well as the extent of its breakdown in the body. When body protein breaks down (or "wears out"), the nitrogen is all excreted in the urine and feces. A chemical analysis of these waste products for nitrogen is all that is needed to compute how much protein has been lost by the body.
When the intake and output of nitrogen are equal, the body is in "nitrogen balance". The amount of protein required daily depends largely upon (1) The calorie intake; and, (2) The quality or biological value of the protein. If the intake of calories is too low, the body is forced to make up the deficit from its own stores, including the proteins; the result is an increase in protein breakdown. In order to conserve the body stores of protein, therefore, it is necessary to provide enough calories to meet current needs. Since the value of a protein is determined by the presence in the molecule of a proper proportion of the essential amino acids, if one of them is low in relation to the others, the body will waste the amino acids that are in excess. The lower the biological value of a food protein the greater the amount that must be eaten in order to maintain nitrogen balance.
What does this mean in practical terms? The National Research Council has recommended that the daily intake of protein for an adult man should be 1 gram per kilogram of body weight (or about 2.5 oz. for the average man). This is the amount contained in 6 eggs or 10 oz. of meat. For adolescent children and pregnant or lactating women, the allowance should be increased by as much as 50%. These allowances are rather generous when the proteins are of good quality. The best practical means of assuring an adequate supply of good protein is to consume a varied diet that contains both animal and vegetable matter.
The protein requirement of man is one of the most important factors in nutrition. Of all the foodstuffs, protein is the scarcest and the most expensive. Hundreds of millions of the earth's inhabitants get neither the amount nor the quality of protein that is required for health and vigor. In view of the alarming increase in world population, the urbanization of our farmland and the rapid erosion and depletion of topsoil, it is difficult to take an optimistic view of the future. The daily arrival in the world of 180,000 new mouths to feed poses problems that will not easily be solved. With sound information on our exact requirements, agriculturists can be informed about what crops will give the greatest return—not in terms of dollars, but in terms of nutritional values for his fellow man—and we can share more equitably the world's production of protein.
Fat and Carbohydrate Requirements
Fat and carbohydrate serve chiefly as body fuel. The need for these foodstuffs varies according to the need for energy, and there is no minimum requirement. Protein usually does not furnish more than I5% of the daily calorie intake, leaving 85% to be furnished by fat and carbohydrate.
The diet may be high in fat and low in carbohydrate or vice versa without upsetting the normal individual; but if the fat content of the diet becomes very high (85% or more of the nonprotein calories), the body has difficulty in burning it completely. When the fat is very low, there is danger that the body will fail to get enough of the unsaturated fatty acids or fat soluble vitamins. Furthermore, a diet very low in fat is not very satisfying—it doesn't "stick to the ribs." The body seems capable of utilizing any fat that can be digested and absorbed. Hence, there is no scale of biological values for different fats. It is always desirable to have some carbohydrate in the diet because it is the cheapest source of calories, and it assists in the burning of fat. It is quite possible, however, to subsist on a diet that does not contain any carbohydrate. The Eskimo diet is a good example of this, and an arctic explorer demonstrated that he could live safely on a similar diet right here in the United States. He and one of his colleagues lived on nothing but meat and fat for a whole year without showing any signs of ill health; but this type of diet is not recommended because the absence of carbohydrate results in an incomplete combustion of fat, which may cause headache, a feeling of muscular weakness, irritability and fuzzy mental processes. (For a discussion of the Eskimo diet, click on Straightdope.)
The amount of carbohydrate needed daily is, like fat, regulated by the demand for energy. If a person works hard or is exposed to cold, his need for calories increases; and the logical way to meet this need is to eat more carbohydrate and fat. These foodstuffs may be regarded as the elastic portion of the diet to be expanded or contracted according to the need for calories.
Fiber, though it does not contribute energy, is also an important part of our foods. It has two main components—insoluble and soluble. Insoluble fibers do not dissolve in water, while soluble fibers dissolve or are broken down in the body. Both types have advantages in the diet. Insoluble fibers provide more bulk to the stool, and they may also play a role in reducing the risk for certain types of cancer. Soluble fibers have been proven to have a lowering effect on blood cholesterol levels.
The Vitamin Requirements
Fifteen or 20 different vitamins are necessary in the diet of man, and most of these must be obtained in the food; but some may be supplied in part by the bacteria that live in the intestine. A large number of bacteria normally inhabit the lower portions of the intestine; and, in the course of their growth, they seem to produce certain vitamins in excess of their own needs and thus make available to their host a small supply of much needed material—a rather gracious gesture in return for hospitality.
In terms of weight, the daily requirement of any vitamin is very small. The amounts of thiamine (the anti‑beri‑beri vitamin), niacin (the anti‑pellagra vitamin), and ascorbic acid (the anti‑scurvy vitamin) may be taken as examples. If the daily requirements of these vitamins are expressed in terms of the weight of a pin‑head (15 milligrams), the following values are obtained: thiamine 0.1, niacin I.0 and ascorbic acid 5.0 pin‑heads respectively. In 1973, the Food and Nutrition Board of the National Research Council assembled a table of daily allowances for most of the vitamins. The project was initiated to serve as a guide in large scale group feeding as practiced in the armed services and industry, and the Council now reviews their recomendations (now called "the reference daily intake") every five years.
The importance of the vitamins is far out of proportion to the small amounts required. It is absolutely essential that the vitamins be taken in quantities sufficient for the body's needs, however small—there are no substitutes. Chemists have attempted to produce substitutes by synthesizing compounds that are very closely related chemically to the vitamins, but the substitutes do not have the same effect in the body as the vitamins; and, in fact, they may be quite antagonistic and tend to bring on the very vitamin deficiency it was hoped they might prevent. Many bactericidal drugs work on this principle and are successful because they induce fatal vitamin deficiencies in the bacteria. It should be emphasized that the chemists have been brilliantly successful in synthesizing the vitamins themselves. The synthetic vitamins cannot be distinguished from the natural ones.
It is impossible for most people to accurately measure their daily intake of vitamins. However, in everyday practice, a sufficiency of vitamins is assured by eating a well rounded diet. For the fat soluble group, which includes vitamins A, D, E and K, it is well to include the green leafy plants such as collards, broccoli and spinach. Young children, who usually don't eat very much of these bulky foods, are sometimes given cod liver oil, or other fish liver oils, to increase their intake of vitamins A and D. Vegetable oils and margarine are excellent sources of vitamin E. A considerable portion of the vitamin K is furnished by the bacteria of the intestine.
Among the water soluble vitamins, ascorbic acid (vitamin C) may be considered separately because it is not usually associated with the B vitamins. The citrus fruits—oranges, grapefruit, lemons—as well as tomatoes, are excellent sources of vitamin C; and a large share of the day's need is met by drinking a glass of fruit juice for breakfast. The family of B vitamins is too large and complex to consider here in detail. Very often the members of this family occur together in nature so that a good supply of one vitamin of the group usually, but not always, assures a good supply of all of them. Two outstanding sources of the B vitamins are brewers' yeast and liver. The cereal grains are probably the most important everyday source. The highest concentration occurs in the germ and outer covering of the grain, and these are usually removed during processing; but, despite this fact, the large consumption of cereals accounts for a considerable portion of the daily intake of B vitamins. Thiamin is found in large amounts in pork; riboflavin is present in large amounts in milk; and niacin is abundant in all meats.
It is evident from the previous paragraph that the vitamins are widely distributed in nature and that no single source is adequate to meet all of the needs for man. This emphasizes again the need and desirability for us to eat a diet that contains a great variety of foods. If each person accepted this idea as axiomatic and applied it to himself every day, there would be very little illness traceable to poor nutrition. Every housewife may have her own idea about what constitutes a varied diet, but each day's menu should include a portion from each of the following "basic seven" food groups: (I) Green and yellow vegetables; (2) Oranges, grapefruit and tomatoes; (3) Potatoes or other vegetables and fruits; (4) Milk and milk products; (5) Meat, poultry, fish and eggs; (6) Bread, flour and cereals; and, (7) Butter and fortified margarine.
There is an ever increasing supply of unreliable fad diets, and they can be classified as either of two types. The first (positive) type develops from a fanatic belief in the magic power of certain foods to correct all defects of nutrition. This faith may rest on the alleged virtues of one food—such as onion juice, soy beans, cranberries or any other item. The second (negative) type avoids many foods on account of prejudice, supposed incompatibility, or plain ignorance. Many people fall for the latter category because they were brought up on very plain fare and haven't enough sense of adventure to try something new. Either type of food fad is quite likely result in a one‑sided diet—and is, therefore, lead to a dietary deficiency.
Most of the mineral salts found in the sea are required in the human dietary. Like the vitamins, they are required only in small amounts. The outstanding exceptions to this rule are sodium chloride (table salt), calcium, magnesium, and phosphorus. Exact information is lacking about man's daily requirement for some of the trace elements that occur in his tissues. Iodine, zinc, aluminum, manganese, copper, selenium and cobalt represent only a few of them. It seems quite possible that poor agricultural practice will deplete the soil of some of the mineral salts that are present in small amounts. It is common knowledge that certain areas are deficient in iodine and that this element must be supplied by adding it to table salt or drinking water; but, for most of the essential elements, depleted soils deprive the plants of needed minerals, leading to stunted plant growth and low crop yields, more-so than depleted food sources.
The practical guide for assuring an adequate mineral salt intake is the same as for the other nutrients—a varied diet. In addition to variety in foods it is probably wise to get them from various sections of the country, representing as many different types of soil as possible.
Clink on Government Guidelines for USDA recommendations.
Note: For nutrient content of specific foods, click HERE.