Diabetes: Its Cause and Its Treatment With Insulin

by Russell M. Wilder

THE NATURE OF DIABETES

Diabetes a disorder of metabolism.—What is this insulin and what does it do? Before this is answered, the nature of the chemical disorder that is called diabetes must be somewhat understood, and to supply this understanding, a partial review of the chemistry and physiology of nutrition must be made.

The processes of life are largely chemical. The warmth of the body is provided by combustion, oxidation of food. If the supply of food is discontinued, life ends, and the body cools exactly as a gasoline motor stops and cools off when its supply of fuel is exhausted. Similarly, if the machinery for transforming food into energy is impaired, life will lag. This is what happens in diabetes; the disorder is much like that of a motor which misses fire when its ignition system is out of order. Food, like gasoline, contains energy, and life results from the conversion of this potential energy into body heat and muscular activity. The processes involved in this conversion are spoken of collectively as “metabolism.” Diabetes is a disorder of metabolism. There are other disorders of metabolism, but none so common as that of diabetes.

Carbohydrate, protein and fat.—The food supply of mankind is limited to the tissues of plants and animals, and the fuel in all such foods is either a carbohydrate, a fat, or a protein. Carbohydrates are starches and sugars; fats are oils, lards and complex materials such as may be found in brain, and egg yolk; protein is abundant in lean meat and cheese. Compared to the protein, the carbohydrates and fats are relatively simple chemical substances, fairly stable and, hence, easy to study chemically. Proteins are excessively changeable, to which character they owe their name. Some proteins are called albumins. Egg albumin, egg white, is a typical protein possessing all of the essential protein characteristics. The carbohydrates and fats serve chiefly as fuels, while the proteins, besides providing energy, build or rebuild the living tissues of the body. A diet may be deficient in either fat or carbohydrate, and still remain adequate. It must, however, provide a modicum of protein, since parts of the protoplasmic machinery of the tissues are constantly wearing out and requiring replacement.

Foods are disintegrated by catalysts.—While the conversion of the energy in carbohydrates, fats and proteins into the life flame is a process of combustion or oxidation, it is not a simple burning or explosion, as in the case of the fuel ignited in the cylinder of the gasoline motor, but proceeds by successive steps or stages. The earliest of these steps is taken in the kitchen where food is prepared by cooking. There the starches are softened and partly broken up, and the proteins are coagulated. The next stages are passed during digestion, beginning in the mouth, where the ptyalin, a ferment in the salivary juice, attacks starches, and continuing as the food passes successively through the stomach and the intestine. Ferments are also called catalysts. At each and every stage of digestion and assimilation some catalyst facilitates and accelerates the process of decomposition in a manner similar to the action of ptyalin on starch, or of yeast in brewing beer. Consequently, the food, before it has descended more than half way down the length of the small intestine, has been disintegrated chemically into fragments that are smaller and, chemically, much less complex than the original foodstuffs. The starches are split into sugars, the chief of which is glucose; the fats are broken into fatty acid and glycerin; the proteins are torn apart and comparatively simpler structures, the so-called amino-acids, result.

Sugar in the blood.—The food fragments resulting from digestion are soaked up through the intestinal wall into the blood and lymph, both of which fluids circulate freely around the intestine, and in the blood and lymph they can always be found, if suitable chemical means are adopted for detecting them. They are abundant in the blood during the hours following meal-taking, and diminish in fasting. The sugar glucose, for instance, is present in blood taken early in the morning in a concentration of about one part in each thousand, or 0.1 per cent, but when carbohydrates are being digested, one and one-half parts of glucose in each thousand, or 0.15 per cent are found.

The rôle of the liver.—The next stages of metabolism occur in the liver, to which the blood passes immediately after leaving the intestine. Here is a veritable chemical laboratory wherein innumerable transformations are worked. Some of them are now understood, and here, as later elsewhere, at every step of change, a catalyst is present to facilitate each separate chemical alteration. Many catalysts are very specific, accomplishing one definite task; others are more generally active. They have been likened to keys, which, fitting into certain locks, permit the locks to be turned. Without these catalysts or accelerators, transformations would occur so slowly that active life, such as ours, would be impossible.

In the liver much of the sugar is removed from the blood and organized into a starch-like substance called glycogen. Thus stored, it is available later, when the blood may be poor in sugar. One of the main functions of the liver is to maintain a nearly constant concentration of sugar in the blood, which it does by subtracting sugar whenever, as after meals, the blood stream is flooded, and adding sugar at those times between meals, and at night, when the sugar level in the blood is low.

In the liver, the amino-acid fragments of proteins are partly destroyed, ammonia is split off from them and changes into a waste product, urea, which is later excreted by the kidneys. Also sugar is made from many of the fragments of protein, and this sugar is either stored away as glycogen with the sugar originating from carbohydrate, or added to the blood. Nearly 60 per cent, by dry weight, of the protein eaten is thus changed to sugar, and as a final result of the normal processes of digestion, and action of the liver, we find that all of the carbohydrate, approximately 58 per cent of the protein, and it is supposed, 10 per cent of the fat of the food, eventually finds its way into sugar.

If we desire to know how much sugar a certain food will add to the metabolism, that is, the sugar value of the food, we must know both the weight of the food and how much of this weight is carbohydrate, how much is protein, and how much is fat. The sugar value will be the sum obtained by adding the weight of the carbohydrate, 58 per cent of the weight of the protein, and 10 per cent of the weight of the fat. For instance, a slice of bread weighing 2 ounces or 60 gm., spread with one-third of an ounce or 10 gm. of butter would be 32 gm. of carbohydrate, 6 gm. of protein and 11 gm. of fat. The sugar value of this mixture would be 32 plus 3.5 plus 1.1 or 36.6 gm. A glass of whole milk, 6 ounces or 180 gm. of milk, would contain 9 gm. of carbohydrate, 5 gm. of protein and 7 gm. of fat, and its sugar value would be 9 plus 3 plus 0.7, or nearly 13 gm.