To determine the energy value of a foodstuff all that is necessary is to burn a given amount of it in such a way that all the heat given off shall be taken up by water. Then, knowing the amount of water and the rise in tem- perature, the number of calories given off can be calculated. Such an apparatus is called a calorimeter, from the word meter, or measure, and color, a Latin word meaning heat. A hollow metal cylinder, containing the material to be burned and a supply of oxygen, is immersed in an insulated tank containing a measured amount of water. Combus- tion is started by sending an electric spark through the foodstuff. The heat given off passes through the metal cylinder into the water. The rise in temperature is very accurately determined by means of thermometers, and corrections are made for any unavoidable escape of heat. All the carbohydrates and fats which are digested and burned in the body give off, so far as is known, the same amounts of energy under these circumstances that they do in the calorimeter. Proteins, however, are not completely oxidized in the body, and so furnish it with a somewhat smaller amount of heat than the calorimeter would indicate. Allowing for losses in digestion, it has been determined that every ounce of either protein or carbohydrate eaten supplies the body with 113 calories of heat; fats have greater fuel value and give 255 calories for every ounce. The total amount of energy which must be supplied per person per day is, obviously, affected by the size of the person whose temperature must be maintained, as well as by the amount of energy used up in work. Atwater, for the United States Department of Agriculture, deter- mined the following amounts as necessary for the man or woman of average size. The woman is allowed less be- cause she averages less in weight. THE AMOUNT OF FOOD NECESSARY 155 Man with hard muscular work 4150 calories Man with moderately active work 3400 calories Man at sedentary or the woman with moderately ac- tive work 2700 calories Man without muscular exercise or the woman at light to moderate work 2450 calories How much protein is necessary daily is still a matter of controversy, but it is well established that the old notion that much meat or protein is necessary for strength is false. Some put the figure higher than others, but 300 to 400 calories a day from protein is probably a safe amount for the average person. In stating the composition of food, sometimes the per- centages of the various ingredients are given. Another way of expressing it is to state the number of calories of heat given by the carbohydrates, fats, and proteins in an amount of food which furnishes a total of one hundred calories of energy. This amount is known as the " stand- ard portion." The second method is perhaps less con- fusing, especially when comparisons between foods are to be made. For example, suppose a boiled potato and white flour are to be compared. The percentage composition of the two is as follows : WATEB PROTEIN FAT CARBO- HYDRATE Boiled potato . . Wheat flour 75.5% 128% 2.5% 10.8% •1% 1.1% 20.9% 74.8% With this great difference in the percentage of water pres- ent, it is evident that the percentages of the other ingredi- ents cannot be compared directly. 156 FOOD STUDY

AI-modernized reading of the original text

To determine the energy value of a foodstuff all that is necessary is to burn a given amount of it in such a way that all the heat given off shall be taken up by water. Then, knowing the amount of water and the rise in temperature, the number of calories given off can be calculated. Such an apparatus is called a calorimeter, from the word meter, or measure, and color, a Latin word meaning heat. A hollow metal cylinder, containing the material to be burned and a supply of oxygen, is immersed in an insulated tank containing a measured amount of water. Combustion is started by sending an electric spark through the foodstuff. The heat given off passes through the metal cylinder into the water. The rise in temperature is very accurately determined by means of thermometers, and corrections are made for any unavoidable escape of heat. All the carbohydrates and fats which are digested and burned in the body give off, so far as is known, the same amounts of energy under these circumstances that they do in the calorimeter. Proteins, however, are not completely oxidized in the body, and so furnish it with a somewhat smaller amount of heat than the calorimeter would indicate. Allowing for losses in digestion, it has been determined that every ounce of either protein or carbohydrate eaten supplies the body with 113 calories of heat; fats have greater fuel value and give 255 calories for every ounce. The total amount of energy which must be supplied per person per day is, obviously, affected by the size of the person whose temperature must be maintained, as well as by the amount of energy used up in work. Atwater, for the United States Department of Agriculture, determined the following amounts as necessary for the man or woman of average size. The woman is allowed less because she averages less in weight. Man with hard muscular work 4150 calories Man with moderately active work 3400 calories Man at sedentary or the woman with moderately active work 2700 calories Man without muscular exercise or the woman at light to moderate work 2450 calories How much protein is necessary daily is still a matter of controversy, but it is well established that the old notion that much meat or protein is necessary for strength is false. Some put the figure higher than others, but 300 to 400 calories a day from protein is probably a safe amount for the average person. In stating the composition of food, sometimes the percentages of the various ingredients are given. Another way of expressing it is to state the number of calories of heat given by the carbohydrates, fats, and proteins in an amount of food which furnishes a total of one hundred calories of energy. This amount is known as the " standard portion." The second method is perhaps less confusing, especially when comparisons between foods are to be made. For example, suppose a boiled potato and white flour are to be compared. The percentage composition of the two is as follows : WATEB FAT CARBO- HYDRATE Boiled potato . . Wheat flour 75.5% 128% 2.5% 10.8% •1% 1.1% 20.9% 74.8% With this great difference in the percentage of water present, it is evident that the percentages of the other ingredients cannot be compared directly.

Food study