In health the ingestion of a mixed diet containing a moderate amount of sugar and starchy foods is not attended by the passage of sugar in the urine. The sugars and starches of the food undergo a series of chemical changes (see pp. 9, 15), being burnt up in the tissues, and forming a source of energy and heat production. In disease there is a defect in the mechanism of digestion and assimilation of carbohydrate foods, with the result that sugar appears in the urine (glycosuria). Even under normal conditions the power of sugar destruction in the body is not unlimited, since if a large excess of sugar be taken in the food, sugar appears in the urine. This is known as alimentary glycosuria. In all probability this alimentary glycosuria is simply the mildest form of the diseased state which in an advanced stage is true diabetes, or diabetes mellitus. In this condition the sugar in the urine is derived from the starches of the food as well as from the sugars. Diabetes may be of a mild or a severe type. In the former the amount of sugar in the urine can be controlled to a very great extent by diet; in the latter, sugar continues to be excreted in the urine, it may be in large amount, even although the diet is free of sugar and starchy food.
In every case in which there is doubt as to the severity of the disease, recourse should be had to a test diet. If a diet free from carbohydrate (sec later) does not cause the sugar to disappear from the urine, the patient is suffering from a severe form of the disease. Care must be exercised in the application of this test, and it is as a rule advisable not to apply this rigid test suddenly; the carbohydrates should be cut off from the diet gradually over a period of several days. In every case we must ascertain what amount of carbohydrate food the patient can tolerate without the appearance of sugar in the urine; in other words, given the presence of sugar in the urine, we must determine whether the condition is one of (a) alimentary glycosuria, (b) mild diabetes, or (c) severe diabetes.
The main essential in treatment is to restrict so far as possible the amount of carbohydrates to the amount which the patient can assimilate without the appearance of sugar in the urine. This involves the use of foods rich in proteins and fats, and the restriction of, or it may be, the abstention from, all sugars and starchy foods. The deprivation of starchy foods in the form of bread and bread foods is a great trial to the patient Most of the substitutes prescribed as diabetic foods are not very palatable; they are, further, expensive, and to many the restriction becomes so irksome that the strictness of the dietary has to be relaxed. The diet must not be regulated exclusively by its effects on the urine. On a given diet the sugar may steadily diminish, while at the same time the general condition of the patient deteriorates. Further, the type of the disease has to be considered. Thus the dietetic treatment of diabetes in an obese adult or in an elderly subject is a simpler matter than the treatment of the severe form of the disease met with in young subjects in whom there is much wasting and general weakness. The weight of the patient is a very important guide in the treatment, and has to be continually noted throughout the progress of the disease. The toleration limit for carbohydrates is another factor to be noted. We must determine the extent to which the excretion of sugar can be affected by dietetic means. A further point that should be attended to is to make the changes in the dietary gradually; in many cases of diabetes there is danger associated with the sudden removal of carbohydrates. Lastly, it is important to make the food as appetising and varied as possible. Assistance in this direction will be found in the description of the Menus on pp. 481 et seq.
In the successful dieting of diabetic patients the principle to follow is to exclude as much as possible the starches and sugars from the food; to replace these important articles of food by fat, which is also a hydrocarbon, so that the body may not lack entirely fuel food. To do this, and still allow the diet to be varied and appetising, requires a considerable knowledge of foodstuffs and cookery.
The main rules to be observed are as follows: -
1. No sugar or articles of food containing sugar.
2. Restriction of all foods that contain starch.
3. The great deficiency caused by the above restriction to be made up by fat, and not by excess of meat.
The lists on p. 473 give the allowable foods, and those that are not permissible, and upon this the menus are framed. It is unfortunately almost impossible to get a satisfactory diabetic diet that is not expensive.
In these tables we see that milk is allowed only in limited quantities, on account of the 4 per cent, of carbohydrate in the form of lactose. This is the most assimilable form of sugar, and in severe forms of diabetes, when there is much impairment of digestion, it is probably often the best food, on account of its protein, its richness in fat, and the solubility of its sugar. If milk is considered inadvisable, an artificial milk can be procured free from sugar (from Messrs Clay, Paget, & Co., Ebury Street, Eaton Square, London; or Messrs Callard & Co., Regent Street, London); this can be diluted with mineral water. Cream has mainly to replace milk in the special cookery, being almost free from lactose, and it has the great advantage in containing the most easily digested form of fat (see p. 40).