Metabolic Diseases

METABOLIC DISEASES. All disease is primarily due to alterations, quantitative or qualitative, in the chemical changes in the protoplasm of some or all of the tissues of the body.

Obesity

(see also CORPULENCE).—It is as fat that the surplus food absorbed is stored in the body; but the power of storing fat varies enormously in different individuals, and in some is patho logical. The reasons of this are probably manifold. One un doubted cause is taking a supply of food in excess of the energy requirements of the individual. The amount of food may be absolutely large, or large relatively to the muscular energy evolved in mechanical work or in heat-production ; but in either case, when fat begins to be deposited, the muscular activity of the body tends to diminish and the loss of heat from the surface is reduced ; and thus the energy requirements become less, and a smaller diet is sufficient to yield the surplus for further storage of fat. Fat is formed from carbohydrates, and possibly indirectly from proteids (see NUTRITION). Individuals probably vary in their mode of dealing with these substances, some having the tendency to convert them to fat, some to burn them off at once. Probably the difference is to be sought in endocrine action. In all cases the fat stored is available as a source of energy, and numerous fat "cures" consisted in giving enough proteids to cover the requirements of the body, with fats and carbohydrates in sufficient to meet the energy requirements of the individual. This is illustrated by the dietaries of some of the best known of these "cures" :— In a normal individual in moderate muscular activity about 3,00o calories per diem are required (see DIETETICS), and there fore under the diets of these "cures," especially when accompanied by a proper amount of muscular exercise, the fats stored in the body are rapidly used up. At the present time such diets are combined with administration of thyroid extract (see MYXOEDEMA, below).

Diabetes

(see also DIABETES MELLITUS; INSULIN), as dis tinguished from transitory glycosuria, is produced by an inability of the tissues to use the sugar presented, which thus accumulates in the blood and escapes in the urine. One great source of energy

being unavailable, the tissues have to use more fats and more proteids to procure the necessary energy, and hence, unless these are supplied in very large quantities; there is a tendency to emaciation.

The power of storing and using sugar in the tissues is strictly limited, and varies considerably in healthy individuals. Normally, when about 2oog. of glucose are taken at one time, some appears in the urine within one hour. In some individuals the taking of even ioog. leads to a transient glycosuria, while others can take 250g. or more and use it all. But even in the same healthy indi vidual the power of using sugar varies at different times and in different conditions, muscular exercise markedly increasing the combustion. Again, some sugars are more readily used than others, and therefore have a less tendency to appear in the urine when taken in the food. Milk-sugar and laevulose appear in the urine more readily than glucose. This power of using sugar pos sessed by an individual is now known to depend upon a due provision of insulin in ordinary cases, but glycosuria after poison ing by carbon monoxide or phloridzin or after puncture of the fourth ventricle of the brain is susceptible of other explanations. The disease may be divided into two forms : I. Slight Cases. The individual can use small quantities of sugar, but the taking of larger amounts causes glycosuria. Sup posing that the energy requirements of an individual are met by a diet of— then if only Ioog. of glucose can be used, the energy value of 3oog., i.e., 1,23o calories, must be supplied from proteids and fats. To yield this, 3oog. of proteids or 132g. of fats would be required. If these are not forthcoming in the diet, they must be supplied from the tissues, and the individual will become emaci ated ; hence a diabetic on an ordinary diet is badly nourished, and hence the huge appetite characteristic of the disease.