The amount of nutrition contained in a given quantity of food is often a determining factor in curative dietetics.

The two most important things to be considered in prescribing foods are:

1 The amount of energy contained in a given quantity

2 The amount of available nitrogen or tissue-building material in a given quantity

Energy

Energy is the power to do work. That form of energy with which we are most familiar is mechanical energy, as raising a stone or turning a wheel.

Heat is another form of energy. Heat and work can be converted into each other. The steam-engine turns heat into work, while a "hot box" on a car-wheel is a case of work being turned back into heat.

Experience shows that a definite amount of heat will yield a definite amount of work, so that the amount of heat produced by a given amount of food, when combined with oxygen, is taken as a measure of its energy. This is ordinarily expressed in calories, a calorie being the amount of heat required to raise the temperature of one thousand grams of water one degree on the centigrade thermometer scale.

Amount of heat a food produces determines its energy

The use of these terms need not concern the student. Instead of using the calorie I will use a unit which is equal to one hundred calories. I have selected a unit of this size because it gives about the ordinary service of food at meals which is easily measured and remembered.

Nitrogen

Nitrogen is the chemical element that is most concerned with the function of life. All animal tissue contains nitrogen, which forms about one-sixth part, by weight, of all the nitrogenous or protein substances.

If we were to take a hundred pounds of lean meat, or muscle, and evaporate from it all the water, we would have about eighteen pounds of dry material left. If we should analyze this dry substance, we would find that about one-sixth, or three pounds, would be the element nitrogen. Thus we say that muscle contains eighteen per cent of protein, or three per cent of nitrogen. In ordinary practise the protein is mixed with fats and salts, and cannot be measured by simply drying out the water, so the chemist finds the amount of nitrogen present and multiplies by 6.25, which gives about the correct per cent of protein. This method is not exact because the per cent of nitrogen in various proteids is not always the same, but it will give an intelligent average. I will discard the use of the term protein, and refer to the amount of nitrogen directly.

Proportion of Nitrogen in lean meat.

All compounds of the element nitrogen are not available as food. For example: The nitrogen of the air, of ammonia gas, or gunpowder cannot be utilized in the animal body. The nitrogen in foods only refers to available nitrogen. Compounds containing other forms of nitrogen are not foods, but are frequently poisons.

Systems Of Food Measurements Compared The "Old" System

Under the old system of food measurement, feeding the human body cannot be made a practical science for the masses, therefore a new system becomes necessary. That we may more fully appreciate the value of a new system, let us consider the methods hitherto available.

Suppose a man is using two quarts of milk a day, and wishes to determine the amount of available nitrogen or tissue-building material and energy it contains. Under the old system he must get a book on food analysis, or send to Washington for a Government bulletin. If he does not understand the meaning of the terms and figures used, the tables would be useless to him until he goes to a chemist to have them explained. He is now ready to work out the nutritive value of his milk, and proceeds as follows:

First, he gets the number of cu cm in the milk, thus - 952.8 (number cu cm in 1 quart) x 2 = 1905.6, number of cu cm in 2 quarts of milk. Second, he gets the weight of his milk in grams - 1.032 (number grams in 1 cu cm of milk) x 1905.6 = 1966.57, number of grams in 2 quarts of milk.

He now turns to a table of analysis which tells him that milk contains 3 per cent of protein, 3 1/2 per cent of fat, and 4 1/2 per cent of sugar. As the amount of nitrogen in milk is approximately one-sixth of its entire protein, he would now get 16 per cent of the 3 per cent (.16 x .03 = .0048), which is the percentage of nitrogen contained in milk.

His next step would be - 1966.57 (number grams in 2 quarts of milk) x .0048 = 9.44, the number of grams of nitrogen in 2 quarts of milk.

I will not explain the way in which the energy would have to be figured, but will merely give the arithmetical processes by which the result is obtained:

3 X 4.1 = 12.3 3.5 X 9.3 = 32.55 4.5 X 4.1 = 18.45 12.3 +32.55 + 18.45 = 63.30 1966.57 X 63.30 = 124483.88 124483.88 ÷ 100 = 1244, the No. of calories or energy (heat units) contained in two quarts of milk.

The New Or "Vieno" System

To a unit of food-energy which is equal to one hundred calories (see last paragraph on "Energy"), I have given the name of Vieno, derived from "vital" and "energy," and pronounced vi-en-o. The Vieno system, therefore, will measure all foods by vi-en-os, or units of energy equal to one hundred of the chemist's calories. One vieno of milk is one-sixth of a quart, or two-thirds of an ordinary glass. From this it is readily seen that two quarts of milk will give twelve' vienos of energy, or, if we wish to express it in the chemist's term, twelve hundred calories.

Derivation Of The Word Vieno

The table also states that milk has a nitrogen factor of .8. Therefore, if we wish to know the amount of nitrogen in the two quarts of milk, all we need do is to multiply the number of vienos by the nitrogen factor; 12 x .8 = 9.6, which figure represents the nitrogen consumption expressed in grams. (See explanation of fourth column of table.) These results are practically the same as those obtained by the old system of computation, but expressed in simpler terms. Thus we see that the vieno system of computing food values is unique in its simplicity, and will be a very material aid in putting Food Science on a practical basis.

How to compute amount of nitrogen in food.

Necessity For A Simple System

Things are commonly measured by volume, or by weight. That volume could not be made sufficiently accurate in the measurement of food values is evident. A bushel of lettuce leaves would contain much less food value than a bushel of wheat. Weight would seem to be a fairer way to compare foods, but all foods contain

Neither volume nor weight are correct standards for measuring food values water, which may vary from five to ninety-five per cent. A pound of turnips, which is nine-tenths water, would not be comparable with sugar, which has scarcely any water.

Even if it were not for the water, weight would not be a fair method of comparison because some foods are of more value per pound than others, owing to their difference in chemical composition. For instance, a pound of butter gives about two and one-fourth times as much heat to the body as sugar.

As before mentioned, the two chief food factors which we ought to measure are energy-producing and tissue-building power.

All true foods when assimilated in the body produce some energy. In fact, only such substances as produce bodily energy, when combined with the oxygen taken in through the lungs, can be correctly termed food.

What constitutes a true food.

I have taken this energy-producing power of food as the best basis for measurement and comparison. The nitrogen could have been taken as a unit, and the energy figured by a table, but it is simpler to use energy as a unit (as given in column 3, p. 655), and figure the nitrogen in the various foods by means of a table which gives the amount of nitrogen per unit of energy. (Column 4, p. 655.)

Multiplication of units of energy (column 3) by the nitrogen factor (column 4) is necessary because the ratio of nitrogen to energy is different in each food.