Corpulence, a state of excessive fleshiness, due not to unusual muscular development, but to an excess of fatty deposition in the adipose tissues of the body. (See Adipose Tissue.) The excessive accumulation of fat which constitutes corpulence is influenced by three principal conditions: 1, the rate of physiological waste involved by respiration and exercise; 2, constitutional tendency; 3, character of diet. In rest the consumption of material for muscular force falls to a minimum. Darkness, which favors nervous quiet, sleep, which checks interstitial waste, and a high temperature, which lowers the demand for vital heat, and at the same time rarefies the air and reduces the respiratory activity, are also favorable conditions for laying on adipose, as those who fatten animals for market well understand. On the contrary, bodily activity is unfavorable to corpulence; it, is accompanied by quickened respiration, by which oxygen is more rapidly introduced, destructive changes increased, and carbon, the main constituent of fat, is carried off by the carbonic acid of the expired breath. A low temperature still further favors this tendency by condensing the air respired, so that more oxygen is taken into the system.
The later investigations in physiological dynamics throw still further light upon the destruction of fat by exercise. According to the views at first maintained by Liebig, all muscular force was attributed to the chemical metamorphosis of the nitrogenous tissues. But later quantitative investigations into the amount of force expended, and the amount of accompanying waste, have shown that the latter is insufficient to explain the former; a surplus of force remains to be accounted for. The principle of the correlation of forces here comes, into play, in the conversion of heat into muscular motion; and the combustion of fat being a copious source of heat, we see how free bodily exercise is at the expense of fat, and therefore reduces corpulence. It is probable indeed that the source of muscular power assigned by Lie-big (actual metamorphosis of tissue) plays a much less important part in sustaining bodily activity than has been hitherto supposed. Constitutional predisposition is moreover a powerful element in the case, as in some the tendency to leanness is so inveterate that neither rest nor an excessive oleaginous diet will overcome it, while in others the plethoric predisposition is so strong that it is difficult to counteract it by exercise.
This so-called predisposition to leanness or obesity depends upon the varying capacity of digesting and assimilating the proximate elements of food, and this brings us to the most potent of the influences by which corpulence may be controlled, which is that of diet. (See Banting.) It was believed until late in the present century that the chemical elements are capable of transmutation in the domain of the vital forces; but it is now established that the living system has no such power. It cannot convert one element into another. It cannot generate the materials of which fat is composed; they must be furnished in food. Yet the organism has a very considerable power of transforming alimentary compounds, and may even change them from one type to another if the requisite elements are present. The fat series, embracing all the oily elements of diet, are almost pure hydrocarbons, having but a very small proportion of oxygen and no nitrogen. The sugars, gums, and starches are hydrates of carbon, containing a much larger proportion of oxygen and also no nitrogen. Starch is easily changed into sugar, and sugar may be converted into a fatty compound by loss of oxygen, a change that is often effected artificially in the laboratory.
Corpulence is due to an excess of hydrocarbon in the system, and is of course most •directly favored by oleaginous food, such as fat meat, butter, gravies, milk, nuts, and Indian corn, which contains a large proportion of oil. But although these fatty foods are excluded from the diet, the hydrocarbons may still be elaborated in the system out of the starch and sugar of bread, potatoes, rice, tapioca, arrowroot, and various other vegetables, fruits, and roots. If these be freely indulged in, corpulence can be promoted under a regimen which strictly excludes the fatty constituents of diet. The predisposition above referred to consists in constitutional tendencies to carry on these transformations. Leanness may be due to a low power of digestion, to a defective capacity of assimilating fats, or a want of ability to turn starch and sugar into fat; while on the other hand strong digestion and vigorous assimilation may tend to produce a surplus of oily material which remains unconsumed. Alcoholic stimulants, which quicken the vital processes, increase digestion, and perhaps furnish hydrocarbon for respiration, are generally favorable to the deposit of fat. Physiologists also assert that the free use of aqueous drinks is promotive of fattening.
The most effectual way to prevent corpulence, therefore, is by a regimen that rejects all those substances that are convertible into fat. If this practice is strictly pursued, it is certain to reduce obesity. It may be necessary to live upon an almost exclusive nitrogenous diet, as the azotized principles fibrine, albumen, and caseine, which go to renew the waste of the tissues, are not convertible into fat. A purely nitrogenous diet, however, would be fatal, and is impossible with the employment of ordinary foods. Aliments that are mainly nitrogenous are still associated with small but variable proportions of starchy and oily principles. A normal diet, as indicated by Liebig, requires the proportion of tissue-forming to respiratory principles to be in the ratio of 1 to 5 or 6. A diet for reducing corpulence will simply reduce the non-nitrogenous substances much below this standard. A strict regimen of lean meat, lean fish, cheese, peas, beans, cabbage, turnips, and acidulous fruits which are low in sugar and starch, if thoroughly carried out, is certain to diminish corpulence. It is proper, however, to state that according to the latest physiology the fats have a very important function in promoting the healthy nutrition of the nitrogenous elements.
Consumption is held to consist in the defective assimilation of pulmonary tissue, and an oleaginous diet is prescribed as a remedy for this malady. Cod-liver oil is administered, not because it has any specific virtue in curing consumption, but because it generally proves easily digestible when other fatty substances fail to be freely assimilated.