Part 12

The student should remember that not only the quantity but the quality of food must be considered. The vieno system of food measurement, as herein explained, is the simplest system of food measurement that has ever been published. It is amply complete, and accurate enough for the purpose for which it is intended, and that is the calculation of the energy and the available nitrogen contained in natural dietaries.

This measurement is really a quantitative measurement; that is, it measures the quantity, not the quality. In order to have a full knowledge of a bill of fare, it is necessary to know, in addition to the quantity, the exact chemical nature of each particular food, and also to know the other foods with which that food will combine.

This food table tells accurately the amount of energy that may be derived from food by chemical analysis, but it does not tell the amount of energy that the body must expend in the work of assimilation. This cannot be given in a table, because it varies with the individual and the condition of his digestive organs.

LESSON XIV

VIENO SYSTEM OF FOOD MEASUREMENT

LESSON XIV

VIENO SYSTEM OF FOOD MEASUREMENT

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.

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.

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: