Measure Of Nutritive Value Of Food

The nutritive value of any given food stuff is measured by the amount of heat liberated during its oxidation into those chemical combinations in which it is to leave the organism.

The unit of measure is the calorie, which is equivalent to the amount of heat necessary to raise one kilogram of water one degree centigrade, or what is nearly the same thing, one pound of water 40° Fahr.

Taking our common food materials as they are used in ordinary diet, the following general estimate has been made of the energy furnished to the body by one gram, or one pound, of each of the classes of nutrients.

Protein, fuel value, 4 calories per gram, or 1,820 calories per pound.

Fats, fuel value, 8.9 calories per gram, or 4,040 calories per pound.

Carbohydrates, fuel values, 4 calories per gram, or 1,820 calories per pound. (Atwater.)

It will be seen that the fuel value, or capacity for yielding heat and mechanical power, of a pound of protein of lean meat, or albumen of egg, is just about equivalent to a pound of starch, or sugar (carbohydrate), and a little over two pounds of either would be required to equal a pound of the fat of meat or butter. It is evident, then, that the fuel value of food depends upon the amount of actual nutrients, and especially upon the amount of fat, it contains.

Atwater estimates "that an average man, at moderately active labor, like a carpenter or mason, should have about 115 grams, or 0.25 pound, of available protein and sufficient fuel ingredients, in addition, to make the fuel value of the whole (day's) diet 3,400 calories; while a man at sedentary employment would be well nourished with 92 grams or 0.20 pound of available protein and enough fats and carbohydrates, in addition, to yield 2,700 calories of energy.

In calculating dietaries it is considered that the food of a woman, or a boy from fourteen to sixteen years of age inclusive, should provide 0.8 the fuel value of a man's food at moderate muscular labor; a girl fourteen to sixteen years of age requires 0.7, a child ten or thirteen, 0.6, a child six to nine, 0.5, a child two to five, 0.4, respectively, in fuel value of the food of a man at moderate muscular labor.

In making dietary studies for a week or more, begin with a certain quantity of food products, the weight of which is known, add to this the weight of all articles purchased during the period, then, when the "study" is completed, deduct the weight of all articles remaining on hand. The difference gives the weight of the articles used. Deduct from each article the weight of refuse left upon the plates, and the amounts actually consumed will be known. Then by the use of the tables showing the composition of the several articles, the fuel value of the protein, fat and carbohydrate in each article may be determined. A simple example in addition will give the fuel value of each nutrient (food principle) for the week. These figures will demonstrate whether the week's food has been "properly balanced" and show wherein the deficiency or excess lies.

In actual practice this work may be shortened and simplified, as the tables given at the head of the respective chapters in this book give the fuel value of a pound of each foodstuff, and this quantity multiplied by the number of pounds consumed gives the total fuel value of both protein and carbohydrate. Then, when the quantity of protein has been determined, the solution is simple. To illustrate, menus have been worked out below for a family of six for one day. The manner of determining the amount of protein and fuel value of one or two articles will suffice for all.

In the breakfast menu, boiled eggs are given; eight eggs weigh one pound; by consulting the chapter on eggs, it will be found that 13.1% of a pound of eggs is protein, that is, the decimal .131 represents the protein in the eggs. The fuel value, is given as 635 calories.

Take mashed potatoes in the dinner menu (see table in chapter on Vegetables), the protein in potatoes is given at 2.5% and the fuel value as 440 calories per pound respectively. Thirty-seven thousandths and 660 represent the value of the protein and the fuel value of a pound and a half of potatoes. The protein in butter is too small in quantity to consider, the high percentage of the fat gives a fuel value of 3,605 calories to a pound. An ounce yields one sixteenth of this, or 225 calories. Six ounces of milk is three eighths of a pound, three eighths of 3.3 (protein) and 325 (fuel value) gives .012 and 120 as the quantity of protein and calories of fuel in the milk. By adding the figures in the columns representing the protein and calories of fuel value, the amount consumed by the family and the calories released in energy is determined; dividing by four gives the proportion for one man.