Fat
Aiton's Encyclopedia (1910)
in the arts and sciences, any substance capable of making a grease spot on paper. In popular usage a fat differs from an oil in being solid at ordinary temperatures. The chemist regards any substance as a fat that will unite with lye to make soap. In their chemical makeup, fats consist of hydrogen, carbon, and oxygen--the same elements of which sugar and starch are composed, although in different proportions. The percentage of carbon is higher. Fats contain glycerin. Plants make fat out of the substances which they draw from the earth and air. Animals store up the fat which they obtain from their food. They also manufacture fat,--especially from starches and sugars. Some fat is necessary to animal life in order to give suppleness to the muscles and other tissues. In persons and animals alike, the tendency to store up fat is greatest in the young, and in those who have reached middle life. A certain variety of sheep is remarkable for storing up fat in the tail to the extent of thirty or forty pounds. The bear and other hibernating animals store up fat in the autumn before going into sleeping quarters for the winter. The system draws upon this fat for support. The camel has the faculty of storing up fat in its hump, to be drawn upon during long journeys. When exhausted by travel and fasting, the hump wrinkles down into a flabby fraction of its former size. Fat is a producer of heat, rather than of strength. The farther people live from the tropics, other conditions being equal, the fonder they are of butter and cheese. The Eskimo, for instance, eats great chunks of raw blubber with the greatest delight. He would rather eat a tallow candle than a piece of candy. The percentage of fat in the carcass of animals varies from fourteen to forty-five per cent. A fat steer may be one-third fat. A fat hog is nearly one-half fat. See Oil ; Seal ; Whale ; Food ; Olive ; Perfume; Gas ; Carbon ; Butter ; Milk ; Palm
What Has Changed in the Last Century
Aiton's 1910 definition by grease spot and soap-making still works as a rough test, and the basic account of fats as carbon-hydrogen-oxygen compounds containing glycerin is correct: fats are now understood as triglycerides, three fatty acids joined to a glycerol backbone. What 1910 could not say is that particular fats are indispensable rather than merely useful for giving "suppleness to the muscles": in 1929 George and Mildred Burr showed that animals deprived of linoleic acid sicken, establishing the essential fatty acids, and fat was also found to carry the fat-soluble vitamins A, D, E and K. The sharp modern distinctions between saturated, unsaturated and artificial trans fats belong entirely to the following century; industrial trans fat, once ubiquitous in shortening and margarine, was ordered out of the American food supply by the FDA in the 2010s. Most striking of all, body fat is no longer regarded as inert storage: the discovery of the hormone leptin in 1994 made adipose tissue an endocrine organ that signals to the brain about the body's energy reserves.
Written for this edition, 2026.