To the average housewife the modern literature on food, with its terms and calculations far removed from her experience and knowledge, reads so much like a textbook of mathematics, that at the mere mention of "calories" she metaphorically "throws up her hands" and banishes all further thought of scientific cookery. As a matter of fact many of the discussions of food, which involve the question of calories and the resulting calculations, are absolutely impracticable for ordinary use and overlook certain fundamental conceptions in the question of dietetics. For example, through the experience of years housewives have built up a series of food combinations which, when examined according to scientific standards, prove to be properly balanced in regard to the various foodstuffs and to have the approximate number of calories to provide a sufficient diet. We find, for example, meat is served with potatoes almost universally, an approximate balance of foodstuffs, or rather a start towards that end. In other words the experience of the household has shown that certain combinations and certain amounts of food keep the family in health and furnish the necessary material for repair of the body and for growth. What the scientists have been doing in the past generation has been to check up practice and place it upon a formal basis so that rules for diet might be formulated.

Now to make it possible to eliminate guess-work from cookery and dietetics and enable us to figure out the whys and wherefores of the customs of the kitchen with absolute accuracy it was necessary to invent new terms. So it came about that "calorie" appeared. There is nothing especially complicated about this term and any housewife, in spite of her doubts and apprehensions, can easily acquire all the fundamental conceptions which it needs to add to her considerations in diet. "Calorie" is simply a term of measurement to show how much value a food has in the work the body has to do. The housewife, through practice, is entirely familiar with a gas bill made out in terms of "feet" and probably with an electric light bill in terms of "kilowatts"; also that the automobile is said to have so much "horse power." Few of us could give an accurate definition of these terms, but we accept them as the measure of our gas or of our electric light bill, or of the power of the car, without much thought or consideration. So a calorie is a similar unit of measure, only this time applied to our food. If a scientist is asked for the meaning of the term he will say that "it is the amount of heat which will raise the temperature of so much water so many degrees." He would, however, probably speak more precisely and say the amount of heat which will raise a pound of water four degrees Fahrenheit, but all one needs to know to apply the knowledge "calorie " represents to the household is that each food contains so many calories and we must have about so many of them in our daily diet.

In short, calorie means heat and in this definition we see again that science is merely verifying an ancient tradition based on the knowledge gained from experience. "Cool as a cucumber" is a phrase as old as the hills, but the new science of food values proves its accuracy. The cucumber is cool - lacks heat - for it takes a pound to supply seventy calories. Then we all know the nursery rhyme, "Pease porridge hot," and science shows that it is hot, for dried peas supply us with 1655 calories per pound. And "pease porridge cold, pease porridge in the pot nine days old" is merely another way of saying that the heat units are all there after nine days.

But these facts need in no way confuse us, for it is entirely unnecessary and impracticable to figure out exactly and absolutely the calorie content of each article of diet and the amount of total for the day. The most efficient results will be attained by fixing firmly in the mind the general proportions and general values of the different articles of food and checking up the family ration, roughly, from time to time. The principles of the balanced ration set forth in the preceding pages are, as a matter of fact, entirely sufficient for the introduction of scientific cookery into the household, but a notion of the caloric basis of "food values" is doubtless a help in understanding the problem most thoroughly.

As we need so many feet of gas to run the oven in the gas stove for baking, so we need so many calories of food value to run our bodies each day. Perhaps it is easier to understand the application of the calorie if we consider that a large slice of bread, a large potato, an ordinary pat of butter, a shredded wheat biscuit, two ordinary graham crackers, or a small lamb chop each furnishes approximately one hundred calories in the daily ration. With these measures as a basis it is not so difficult to understand what is meant by saying that the average adult needs from 2500 to 3000 calories in the food of his daily ration. We all know from experience and observation that a woman neither requires nor eats as much food as a man and her requirements have been estimated at about two-thirds that of the man. Another way of figuring is that the body needs so many calories for so much weight, and this brings the same result for a woman on the average obviously weighs less than a man. So children require less food than the adult and so on. The requirements for food which the scientists have laid down simply put into mathematical form the facts most of us have known and put more or less into practice.

A rough estimate of food requirements is about as follows:

A man without work ....................2450 calories

A man doing moderate work..............3000 calories

A man doing hard work....from 3400 to 5500 calories

At first glance it may appear that there is not the expected difference between the requirements of a man doing little work and one doing a great deal. But we must remember that the largest part of our food is used up in the unconscious activities of the body. Even when we are asleep the body is using up the energy derived from the food so that the unconscious demands require a considerable supply of food in themselves. Another vagary of the bodily mechanism is that brain work requires little or no energy from our food. This is why professional men should limit their food intake far below that of the day laborer.

Perhaps the matter of the amount of food required may be summed up by saying that the average man needs from three to four pounds of food a day - this, of course, including bulky foods of a low caloric value - proportioned according to the principles of the balanced ration. For it is not sufficient that the food total the 2000 or 3000 calories required; they must be proportioned properly among proteins, fats and carbohydrates. Most of the dishes which appear on our tables combine the foodstuffs in some proportion or other. One has only to glance at a steak, for example, to realize that it must contain fat in addition to the protein which is its preponderating element. It is now believed that the food elements should appear in about the following proportions: 16 2/3% protein, 25% fat, and the balance, or 58 1/2%, carbohydrates. In other words we should eat half as much again fat as protein and two and a half times as much carbohydrates as fat. The principal point of difference is about the protein, some authorities contending that eight per cent of protein in the diet is sufficient.

But in estimating the demands for the three foodstuffs it should be remembered that all the food which we take in is not available, only about three-quarters of the protein, for instance, being used in the body, so that a certain excess beyond the theoretical requirements is probably desirable.

From the foregoing we may estimate the daily food demands as follows: