Some tropical diseases, such as sprue and dysentery, are in the main best treated by modifications in diet, whilst in other tropical diseases diet is of subsidiary importance, and in others again errors in diet are causes of relapse or of grave complications.
In tropical countries the normal diets of the European and native inhabitants respectively differ more than do those of the various classes of the inhabitants of temperate climates. The effects of dietetic errors in Europeans in the tropics are, on the whole, more marked than would be the case from similar errors in temperate climates; this is specially so as regards the abuse of alcohol and condiments, and also as regards deficiency of fresh vegetables, of fruits, and occasionally of meat.
Frequently the European in the tropics does not modify his diet sufficiently, and does not make adequate use of the local vegetables and other native material. The meats and fruits there are sometimes comparatively dry and tasteless, and the vegetables are apt to be indigestible and of inferior quality. More thorough cooking and also higher spicing of the dishes are frequently resorted to and a larger variety of methods of preparation employed. As a result the bulk of food taken is as much or even more than in Europe, and protein material, not always in a very digestible condition, forms too large a proportion of the dietary.
Moreover, as less active physical work is usually performed, and as the heat production required to maintain the body temperature is less, the result is that an excess of food material is ingested which has to be excreted or more or less injuriously assimilated. The excretory organs are thus unnecessarily taxed and owing to the usual free diaphoresis the fluids taken are insufficient to flush the kidneys properly, or to secure adequate excretion of the solid products by that channel. The liver may become abnormally congested and in many cases nervous symptoms, similar to those attributed to uric acid poisoning, may develop. In other cases the digestive organs fail and chronic atonic dyspepsia, dilated stomach, chronic constipation, or less commonly chronic diarrhoea, sometimes of a lienteric character, are the consequences. Copious draughts of water, of aerated waters, and iced drinks are also a fruitful source of dilatation of the stomach and of gastric catarrh.
Another potent cause of tropical dyspepsia is the use and abuse of drugs, such as quinine. As a prophylactic this drug is still necessary in the more malarial districts where other preventive measures have not been instituted or are ineffective. Its persistent employment in this way may lead to a form of atonic dyspepsia, or of gastric catarrh.
Many of the conditions known popularly as " tropical liver " are due to dyspepsia produced in one or more of these ways, possibly in some instances complicated by alcoholism.
Many tropical diseases, such as repeated attacks of malaria, bring about mental depression and indifference to food. Under such conditions food may be taken irregularly and in insufficient quantities, and little attention may be paid to the quality or the cooking. These circumstances may lead to alcoholism, as the sinking feeling so commonly felt is temporarily relieved by stimulants.
Some of the effects of these various conditions are slight in young and healthy adults. In others, even in those who live an open-air life, and who take plenty of active exercise, although they may not be seen at first, they may manifest themselves after several years of apparent immunity. In persons living a sedentary life, and particularly in many women, there is no such counterbalancing physical activity; these suffer early and usually severely.
The treatment of such dyspeptic conditions is difficult if one is restricted solely to dietetic measures. Patients rarely consult the medical man in the early stages when regulation of the diet and life would result in speedy cure. Even when the condition is well established, a simple nutritious diet consisting mainly of milk, fish and fresh vegetable food (native if fresh European vegetables are not to be had), and such fruits as can be obtained, together with temperance or total abstinence in the matter of alcohol, will often result in marked amelioration. Change to a temperate climate is in the majority of cases necessary, and even without restriction of diet marked improvement usually follows, whilst with a carefully regulated plain liberal dietary, complete recovery may be anticipated. The worst cases, however, should be sent to such health resorts as Harrogate, Carlsbad, Homburg, Vichy, and the like, where the combination of a regular life and restricted diet together with carefully regulated exercise, aided perhaps by the waters, will usually restore the health completely. Dyspeptics of this description should not return to the tropics if it can be avoided.
With wealthy natives a similar condition is not uncommon. The actual diet will be different, and the excess of food taken will be not in protein only but in fatty substances also. Although such natives will probably use more highly spiced and flavoured condiments, they are less likely than the European to abuse alcohol. The effects, however, are similar, except that in the native the tendency to obesity is greater and, as little active physical exercise is taken, appears early. Such patients do not submit readily to restrictions in their diet or course of life. The indications, however, are clear; these are to reduce the amount of fats and proteins and to increase the amount of uncooked vegetable food. If this course can be combined with increased exercise, or, if this cannot be done, with long carriage drives, amelioration frequently results.
With the mass of the native population the dietetic errors are mostly due to poverty. As a consequence, there is more or less deficiency in the more expensive protein and fatty foods. The protein and fats consumed are in the main derived from the comparatively cheap vegetables, whilst the bulk of the diet consists of the cheapest cereal available. Rice is the main support of a large portion of the population, and in times of scarcity may be absolutely the only food taken. On such a diet life can be maintained and even vigorous work performed, but the relative proportions of protein, fat, and carbo-hydrate are such that a great strain must be thrown on the digestive powers. In some districts even rice is too expensive for the impoverished population. Sweet potatoes, yams and similar innutritious vegetables become the staple food, with the result that enormous quantities are of necessity ingested, and the stomach becomes permanently dilated from recurring overdistension.