The Food Unit Or Calorie

Of the seven food classes three are oxidized in the body and may be measured by the calorie or heat unit. In this way we may as easily measure our body intake of fuel as can the manufacturer who estimates the amount of coal necessary to furnish the energy required to run the machinery of his plant. Every ounce of protein, fat, or carbohydrate taken into the tissues produces a definite amount of heat. Heat can always be converted into energy.

The Calorimeter

The instrument used in measuring the heat value of food is called a calorimeter, and simply described is this: - A double chamber, in the inner chamber a given quantity of food, e. g. an ounce of sugar; in the outer chamber a given quantity of water of a known temperature. The food in the inner chamber is ignited by an electric spark. When the burning is complete the temperature of the water in the outer chamber is taken and the increase in temperature shows the energy or caloric value of that food.

The Calorie

The amount of heat required to raise the temperature of a pound of water 4 degrees Fahrenheit, or 1 degree centigrade is a calorie. The slow combustion of an ounce of food in the body tissues will produce the same amount of heat as though oxidized rapidly in a calorimeter. By experiment it has been found that the heat value of a gram of pure water-free protein, e. g. the casein of milk, egg albumen, fibre of meat is four calories; of a gram of pure carbohydrate as starch or sugar, four calories; but of a gram of fat more than two times as much, or nine calories.*

♦More accurately - 1 gram of protein equals 4.1 calories; 1 gram of carbohydrate equals 4.1 calories; and 1 gram of fat equals 9.3 calories.

An ounce equals about thirty grams, therefore multiplying the above figures by thirty, gives the number of calories per ounce. Different foods contain varying amounts of these oxidizable substances; accordingly the caloric value of food stuffs depends upon the amount of protein, fat or carbohydrate they contain; e. g. an ordinary slice of bread weighing 1 1/4 ounce, or 38 grams, contains approximately 4 grams of protein, 2 grams of fat and 16 grams of carbohydrate, the 16 grams remaining being water and cellulose.

Or approximately 100 calories.

By a little study one may very easily become familiar with the approximate values of common foods and be able to arrive at some conclusion as to the correctness of one's daily food ration in its amount and proportion of food elements. Many would be surprised to find how far short their diet comes from the ideal which if followed would result in the maximum of health and strength.

A Practical Application

It is very easy to remember that one slice of bread contains 100 food units, one egg 75, a glass of milk 150, an average potato 125, a tablespoonful of average cream about 40, a serving of cooked cereal 75 to 100 calories, an ordinary serving of green and leaf vegetables 25 to 50, depending upon the amount of fat or milk added, average serving of legumes 100 to 150 calories; also that desserts are higher in food value, ranging from 125 calories for a simple custard or junket to 350 for one-sixth of a pie. See table given below. These and many others in a short time become very familiar to the housewife interested in food values.

Food Requirements

The amount of food required by the individual varies with height, age, sex and muscular activity, but for the average person 2000 calories may be taken as a working basis. One above average height will need more perhaps. Other things being equal, men need about ten per cent more than women. If engaged in active, muscular labor, the requirements may be 2500 to 3000, or even more in the case of a farmer, a lumberman, or a soldier. Those of sedentary habits often do better on less than 2000, even as low as 1500 or 1600. This will depend upon the height, temperament, and natural tissue activity.

An obese individual or one suffering from the results of imperfect oxidation, as manifested in rheumatic joints, high blood pressure, may do well for a time on as low as from 1000 to 1200 food units daily, with marked relief from symptoms and, if obese, a reduction of from one to four pounds per week.

How Much Protein?

The amount of protein needed does not vary within such wide limits. The amount remains more nearly constant and should be from 200 to 300 calories in twenty-four hours, even though the total ration be low. On the average ration this would be about ten per cent of the entire daily food intake, but if one does well on the low ration as suggested above, the protein must not be reduced proportionately but should be kept near the normal of at least 200 calories; for the body, not being able to store this repair material in excess, must have it supplied to it in regular daily amounts.

How Much Fat?

The fat intake should be from 400 to 800 food units per day.* A study of food values soon makes it very evident that the average individual takes much more than this amount in his daily food ration. The remainder of the total calories is made up of carbohydrate. Fat and carbohydrate can to an extent be substituted one for the other, but an excess of fat should be avoided. This we will discuss in a later chapter.

*This need not be in the form of free fat. Many foods contain a high proportion of fat, as milk, eggs, olives, nuts.