A pound of fat has about three times as much fuel value as a pound of wheat flour, which consists largely of starch.
Common examples of fat are butter, cream, the fat of meat and of nuts, and the oil of grains and seeds—notably the cocoanut, olive, and oatmeal.
Fat forms about twenty per cent. of the weight of the normal body.
The body cannot remain in health for long unless a proper amount of fatty food is eaten. Muscular and nerve action, and the formation of the digestive secretions are all dependent on the energy derived from the combustion of fat. Its use in this way spares the tissues from destruction in the chemical processes necessary to life.
Both carbohydrates and fats are composed of carbon, hydrogen, and oxygen, the difference being that there is less oxygen in fat. One pound of starch requires one and one fifth pounds of oxygen for perfect combustion, while one pound of suet requires three pounds of oxygen. One ounce of fat yields two and one-half times as much energy as an ounce of sugar or starch.
Fats are not digested in the stomach. The connective tissue about the fat is dissolved here, and the fat is passed on into the small intestine, where it is acted on by the bile and the intestinal juices. These first change the fat into an emulsion and then into the form of soap and glycerin. In this saponified form, it is in condition to be absorbed and carried to the tissues, where it is assimilated and used in energy. The commercial production of soap from oil is similar to the chemical change in the body of fat into soap.
The supply of fat stored in the body depends on the quantity consumed with the food, on the quantity used up in heat and energy in muscular or mental exercise. The quantity assimilated depends somewhat on the condition of the nerves. If the nerves are weak, they do not strongly direct digestion and assimilation and less fat is used in the digestive and assimilative processes; thus, in case of weak nerves more fat is often stored in the tissues. An excess of fat often indicates sluggish nerve activity.
Manual laborers require more fat for energy than do people whose habits are sedentary. School-children, or children who play hard, should have sufficient fat and sugar.
Butter and Cream. The fat present in milk, depends of course, on the quality of the milk. There is as much butter-fat in a glass of fresh Jersey milk as in a glass of cream from the milk of some cows. The cream from some Jersey cows is eighty per cent. butter-fat.