( Originally Published 1938 )
In the course of our discussion on food, we have pointed out the necessity of eating a certain amount of each element. It is only in this way that you can achieve a "balanced diet", that is, a diet that meets all the requirements of the body.
A balanced diet is one that (a) furnishes enough energy to keep the various functions of the body going, (b) that furnishes material for the building and repair of tissue, (c) that furnishes enough water, (d) that furnishes enough mineral matter, (e) that furnishes vitamins, (f) that furnishes sufficient bulk and (g) that helps to maintain the acid-base balance of the body by furnishing the right amount of alkali-ash and acid ash.
From what we have said on the food elements, it is obvious that the body does not require an equal amount of the different food substances. It is also clear that a growing child needs a larger amount of tissue-building foods than an adult and that a laboring man needs more energy-producing foods than a man working in an office.
Thus it would seem that individually we could arrive at a diet, with a little experimenting, perhaps, that would meet the demands of our own particular systems. Such is not the case, however. If it were, there would be no overweight persons, no underweight ones, no easily fatigued ones and a much smaller number of cases of diseases due to malnutrition.
Fortunately, we now can scientifically calculate the amount of each food element necessary to maintain the body in good health at all ages and in every environment.
Now, no matter how varied the functions or activities of the different cells, they all use up energy. And this consumption of energy is constantly going on, simultaneously with the other functions, including the building and repair of tissues. Indeed energy is needed just as much for tissue building as it is for external and internal work. In the introductory chapter of this book, you will recall, we said that Energy is the basic principle of Life.
What could be more logical, then, than to measure the body's requirement of protein, carbohydrate and fat than by the amount of energy these elements can produce when burned with oxygen? This is exactly how we do determine the amount of food needed.
Now in the creation of energy, heat is given off and it is the amount of heat given off which gives us the measurement of the energy consumed. The unit of measurement is called the calorie. A calorie is the amount of heat required to raise one gram of water one degree centigrade. In measuring the heat energy of the body the large calorie is used that is, the amount of heat required to raise the temperature of one kilogram of water one degree centigrade, or one-pound of water four degrees Fahrenheit.
The different food elements yield each its own number of calories when burned with oxygen. The number of calories is slightly less than the number yielded in a laboratory test because there is some loss through digestion, incomplete combustion and other factors. So, for all practical purposes we can calculate that:
Protein yields 4 Calories per gram Carbohydrate yields 4 Calories per gram Fat yields 9 Calories per gram.
The number of calories a body needs a day varies with age, sex, activity and weight. All these factors affect what we know as metabolism. Metabolism is a general term used to cover all the physical and chemical activities of the body. Energy metabolism the kind of metabolism we are now concerned with refers to those chemical changes which take place when energy substances are burned in the body.
More calories are required by younger people than by old, more by larger than small, more by men than women (although the rate of metabolism is greater for women) and more by physically active persons than those leading sedentary lives. It is estimated that the average sized man uses up about 1700 calories when he sleeps, and the average sized woman, 1400 calories. Work done sitting increases the man's consumption of calories to between 2200 and 2800; a woman's between 1800 and 2200 calories a day. In moderate exercise a man consumes between 2700 and 3000 calories a day, and a woman, between 2200 and 2500 calories. In work requiring great muscular exertion a man may use up between 4000 and 6000 calories.
Generally speaking, we may say that man requires about 2800 to 3000 calories a day and a woman about 2200 to 2500 calories, this amount varying, of course, with the output of work, and with size and age.
That the number of calories should be apportioned among the three food elements protein, fats and carbohydrates is evident from what we said of the other uses these foods are put to in the body, as well as the processes which finally lead to their burning. No fast rule can be made as to the amount of each food consumed. It depends upon the amount of energy expended, the climate, one's digestive powers and many other factors.
The largest number of calories, of course, should be taken in the form of carbohydrates since they are the most economical form of energy. About 60 to 70 per cent of the calories should be in the form of carbohydrates.
Most of us eat too much protein, the average American diet being composed of almost as much protein as carbohydrate. Protein, you will recall, cannot be stored in the body, but the excess must be burned and the nitrogen excreted by the kidneys. This, of course, is done at great expense to the body. Too much protein may also upset the acid-alkali balance of the body, and in addition, frequently causes putrefaction of the intestinal contents. Therefore proteins should compose only 10 to 15 per cent of the diet of an adult in average health.
Fat may compose 15 to 20 per cent of the caloric intake, and except under normal circumstances it is not wise to consume more than this amount, for as necessary as fat is, in excessive amounts it is exceedingly disadvantageous. Too much fat leads to overweight and it is much more difficult to get rid of those extra pounds than it is to put them on. Fat takes a longer time to digest than either proteins or carbohydrates. Thus it naturally causes a slowing down of the emptying of the stomach and the digestion of other foods. This sometimes is of advantage as it insures more complete digestion and staves off hunger pangs. Frequently, however, it may cause indigestion. Moreover, foods heavily coated or permeated with fat may escape digestion and ferment or putrefy in the intestines. Few cooks have mastered the art of frying foods that will be digestible. All too often the fat is heated to such a high temperature that a substance is formed that is irritating to the lining of the digestive tract. It is this irritating substance formed when a fat is overheated that causes most of the cases of indigestion from fried foods, and not the fat itself.
It should be remembered, too, that fat is lacking in minerals, fiber that gives the necessary bulk to the feces, and in most of the vitamins. Therefore, if an excessive amount is eaten you are more than likely depriving your system of these elements so necessary for life and health.
The minerals do not give forth heat and energy and therefore the body's need of them is not measured in calories, but simply by weight, usually in grams or milligrams, and the daily requirement is determined by the amount excreted. Of course the amount varies with many factors. For example a growing child needs more calcium than an adult and a person who is "sensibly" perspiring more than one whose perspiration is not visible.
It is estimated that the average person requires about 5 grams of salt a day, one-half gram calcium, about one and one-half grams of phosphorus, between 6 and 16 milligrams of iron and .00014 milligrams of iodine. Taking them as a whole, and using 100 parts of carbohydrates as a basis of calculation, we require about six parts of mineral matter.
However, there is little need to worry about the mineral matter, provided you are in average good health and are eating a well-balanced diet as far as the other elements are concerned. You're then bound to get your quota of minerals.
But remember this no matter how careful you are about your diet, no matter how fresh the food you eat, no matter how carefully you prepare it, if your intestinal tract is not regularly cleaned of clogging, poisonous waste, you will not get the full value of your food. It will not be properly digested and assimilated and as a result your whole system not only your digestive tract, will function poorly.