This section is from the book "The Human Body: An Elementary Text-Book Of Anatomy, Physiology, And Hygiene", by H. Newell Martin. Also available from Amazon: The Human Body.
The most important of these are stearin, palmatin, margarin, and olein, which exist in various proportions in animal fats and vegetable oils; the most fluid containing most olein: butter contains a special fat known as butyrin. All fats are compounds of glycerine with fatty acids, and, speaking generally, any such substance which is fusible at the temperature of the body will be useful as a food. The stearin of beef and mutton fats is not by itself fusible at the body temperature, but is mixed in those foods with so much olein as to be melted in the alimentary canal. Beeswax is a fat which does not melt in the intestines and so is unabsorbed, although from its composition it would be useful as a food could it be digested.
What nitrogen-containing substances form an essential article of diet? Whence are they obtained? Name the most important albuminous foods.
What foods besides albumens contain nitrogen ? To what extent can they take the place of albumens? How is gelatin obtained? Should we try to build up an invalid's strength on calf's-foot jelly alone? Give the reasons for your answer.
To what group of foods do fats and oils belong ? Name the more important. What is their chemical composition? Why are some fatty bodies not nutritious? Give an instance.
They are mainly of vegetable origin. The most important are starch, found in nearly all vegetable foods; dextrin; gums; grape sugar (found in most fruits); and cane sugar. Sugar of milk and glycogen are alimentary principles of this group derived from animals. All carbohydrates, like the fats, consist of carbon, hydrogen, and oxygen; but the percentage of oxygen in them is much higher than in fats. When oxidized they have therefore less power of combining with additional oxygen than fats, and so are not capable of yielding as much energy to the body.