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Nutrition and Resistance to Disease
Excerpted from Nutrition in Everyday Practice, 1939.
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Nearly a hundred years ago Graves wrote, “Want of a sufficiency or food of an unwholesome or an improper character predisposes the human frame to disease by its debilitating effect on the system”. It is interesting to note that some physicians in the past recognized and emphasized the role of nutrition in the maintenance of health and resistance against infection. No one now questions the role of proper nutrition in resistance against disease. from a clinical standpoint, possibly most of us think of it in terms of under-nutrition rather than of malnutrition. The difficulty of obtaining clinical evidence of the effect of minor nutritional deficiencies is obvious. The story is entirely different however in regard to animal laboratory experiments where all conditions can be adequately controlled.
There is evidence that a lack of almost any one of the 32 food elements essential for animal nutrition will result in a lowered resistance to infection. A number of experiments giving evidence of this nature have been reported by one of us (E.C.R.). The procedure developed was to feed animals with a measured amount of a disease-producing organism and note the number of animals that survived. This sounds like a very simple procedure, but actually it constitutes a most difficult and time-consuming experiment. A suitable disease-producing organism had to be first obtained. After a number of trials, an organism called Salmonella muriotitis (rat typhoid) was found to be suitable for this type of study. It was comparatively harmless for the human being, but in suitable doses was found to be pathogenic for the rat and yet not so severe in its effect that it invariably killed all animals. When death occurred it was preceded by marked diarrhea, cyanosis, and a bloody discharge from the nostrils. Blood cultures were taken aseptically from the hearts of all the dead animals and the organism was regularly recovered, usually in pure culture, indicating that the rats had a muriotitis septicaemia when they died. The animals were observed for 28 days after the infecting dose, when the experiments were terminated, and those that lived for this length of time constituted the survivors. When death occurred it usually was within the first ten days. The degree of resistance was estimated by the percentage of survivors in each experiment. In every case the experimental animals were fed a diet adequate in all respects with the exception of the factor or factors being studied. Control litter mates were fed the same diet with the addition of the substance under study.
In Table I is shown the effect of lack of vitamin A on resistance to infection. It is to be noted that when the diet was deficient in this vitamin only 40 per cent of the animals survived as compared to a survival rate of 79 per cent in the litter mates who were fed the same diet with added vitamin A, in the form of its precursor, carotene.
Table I–The Effect of A Lack of Vitamin A (Carotene) on Resistance to Infection
In Table II it is seen that when the diet was lacking in the vitamin B complex 20 per cent of the animals survived, as compared with a survival rate of 72 per cent when the diet was perfect in all respects.
Table II–The Effect of A Lack of the Vitamin B Complex on Resistance to Infection
Similar results were obtained, as shown in Tables III, IV and V, when the diets were lacking respectively in vitamin D, minerals, and animal protein. In Table V it should be noted that the first lot of animals received their protein from grain sources, while the control animals received their protein largely from milk casein. This is evidence in favour of the advisability of including in the diet each day a certain proportion of protein as animal protein, namely, meats, fish, poultry, eggs, milk and cheese.
Table III–The Effect of A Lack of Vitamin D on Resistance to Infection
Table IV–The Effect of A Lack of Mineral on Resistance to Infection
Table V–The Effect of A Lack of Animal Protein on Resistance to Infection
In considering the percentage of survivors in Tables I to V, no comparison should be made between the number of survivors in one table with the number of survivors in another table, because with each set of experiments it was necessary to regulate the dosage of the Salmonella muriatitis. This was necessary because there was a variation as the experiments proceeded in the degree of virulence of the organism. However, in every individual experiment the conditions of the control animals and of the experimental animals were identical, with the exception that the diet in the experimental group was lacking in the factor or factors being studied.
In the experiments the conditions were naturally quite severe, in that the deficiencies produced were very marked. One might say that deficiencies of this degree would rarely if ever be encountered under Canadian dietary conditions. Further studies were then made in which the degree of the deficiency in the diet was comparatively slight. The results obtained in one set of experiments are given in Table VI. It is seen that with this lesser degree of deficiency there is still a marked difference in the resistance of the two groups of animals against disease. These studies with animals furnish clear-cut evidence that improper nutrition lowers the resistance of the animal to infection and also that the nutritional deficiency does not have to be so severe as to produce outstanding evidence of disease.
Table VI–The Effect of A Partial Lack of the Vitamin B Complex on Resistance to Infection
With this laboratory evidence in mind, that a nutritional deficiency will result in a lowered resistance to infection, how are we going to feed our sick patients? If the illness is an acute one of short duration, simply a matter of 3 or 4 days, this question is not urgent. However, it is obvious that if the patient is suffering from any disease that lasts more than a week or so, special attention must be given to his nutrition as a whole. Strange as it may seem, this is frequently neglected. Recent work has indicated that the presence of any infection increases the need of the body for many of the food elements. To give only three examples; it has been shown that the amount of vitamin A and vitamin C in the blood is markedly lowered by infection, and there is evidence of an increased need for vitamin B1.
The physician’s duty to his patients, however, should not stop with just the treatment of the acute or chronic illness. When the patient presents himself with even some minor infection, our interest should be aroused as to why the infection developed. Was it the result simply of a focus which could have been removed or treated, or have the patient’s habits been such that he is not enjoying the highest level of resistance? Probably the most important of these habits are his habits of nutrition. The remarkable adaptability of the body is such that a person may have a nutritional deficiency for many years before it clearly evidences itself. In the interval, however, the patient will not be enjoying the highest possible level of health and resistance against infection.
One should not expect that infections can be completely prevented by dietary means. This, of course, is impossible, and with many diseases there is no evidence that nutrition has any effect on the susceptibility of the patient to the disease. However, from clinical observations, there is no question that with proper nutrition the patient’s resistance to disease is maintained at a high level and that he will “throw off” or recover from his infection more often and more quickly than the one who is malnourished.
One cannot lay down any rules as to the nutritional treatment of a patient during illness. However, when the patient has recovered, and there is no specific contraindication, his food should include each day a pint to a pint and a half of milk for children, one-half pint for the adult, some meat, one egg daily, two liberal helpings of vegetables besides potatoes, some raw fruit or vegetables, and, during the winter months, some source of vitamin D. If this is done, you will be assisting your patients to reach that goal which we all desire, namely, optimum resistance against infection and optimum health.