It is an integral part of every medical evaluation even when attention is directed primarily to some other phase of a patient’s problem and nutritional therapy is an essential feature in the management of every disease state although it may involve only institution or maintenance of an adequate diet. Unfortunately, the nutritional state of a patient is often taken for granted or dismissed with a cursory observation of the abundance or scarcity of bodily fat. A note may be made in the record “well developed and well nourished” and investigation is pursued in other directions.
In general, medical practice has not kept abreast of the tremendous advances in nutritional science and the refinements in nutritional diagnosis which have been evolved in recent years. It is true that the health hazards of obesity are receiving considerable emphasis and the importance of electrolyte balance is recognized with increasing frequency. Nevertheless, these are only facets, although important ones, in the broad field of nutrition. Vitamins have been prescribed for a wide variety of major and minor complaints, often without reason or justifiable hope of efficaey. Each new vitamin has been heralded as a panacea for many of the unsolved problems of medicine. Such unscientific enthusiasm has resulted in unwarranted scepticism on the part of many physicians as to the importance of vitamins, and of other nutritional factors as well, in the pathogenesis and therapy of disease.
The term nutrition is often considered in a narrow sense as meaning knowledge of the essential chemical substances which must be included in the diet and application of this knowledge to dietotherapy. The science of nutrition embraces a much wider field. Knowledge of the role of essential nutrients in metabolism, which includes the whole realm of nutritional biochemistry, is vital in the understanding of normal bodily function and the many disturbances which occur in disease. Many types of disease, whether infectious, metabolic or de-generative, influence the nutritional state of the patient and, in turn, nutrition influences the prevention, development and regression of many pathologic states.
Nutritional diagnosis means much more than the detection of some overt deficiency disease, a concept prevalent some years ago. Today, it is essential to think less in terms of specific deficiency states and more in terms of disturbances in the biochemical reactions of the body. The diet must furnish the potential energy for basal metabolic processes and for physical activity and, also, all of the chemical substances needed for manufacture of new tissue. Recent investigations, using isotopic techniques, have indicated that the components of cells are constantly being broken down and reconstituted, requiring continuous replenishment with essential nutrients (1). Nutritional diagnosis implies, therefore, evaluation of the biochemical milieu within and outside of the cells, as well as detection of abnormalities of function and structure of the organs and tissues of the body. Recent studies of the role of mitochondria and other cellular units in oxidative metabolism link cytology and biochemistry closely together and may lead to better correlation between pathologic anatomical changes and biochemical abnormalities of body tissues and fluids.
In general, nutritional deficiency occurs gradually although the speed of development varies widely. The reserve stores of nutrients are depleted before biochemical or physiological dysfunction develops. Gross structural changes in tissues are usually late manifestations of severe or prolonged depletion.
Attainment and maintenance of adequate nutrition is not difficult in the United States, since a wide variety of food is readily available. Consequently, the importance of nutrition may not be appreciated sufficiently in this country, except in situations of extreme poverty and neglect or in severe illness. In many countries of the world, serious degrees of malnutrition are common and it is in these areas that the vital role of nutrition in health is demonstrated most strikingly. The importance of nutrition in growth and development, and in the maintenance of physical, mental and emotional well-being throughout life, is attested by natural experiments in endemic areas of poor nutrition as well as by planned laboratory experiments with human volunteers. Minot’s statement (2) that the history of the world might be written in terms of nutrition rather than in terms of epidemics, as in Hans Zinsser’s book Rats, Lice and History, does not seem to be an exaggeration.
The importance of nutrition in conditions of physiologic stress, i.e., in growth, pregnancy and lactation, has been well documented. Recent investigation indicates a close relationship between nutrition and many forms of pathologic stress such as severe infections or trauma. Relationships between nutrition and some of the degenerative diseases, for example atherosclerosis and hyper-tension, and even between nutrition and neoplasia have been demonstrated. It is in this wide variety of pathologic states that nutritional diagnosis assumes paramount importance in well-fed population groups. In rehabilitation from all types of injury, close attention to nutritional problems reaps a rich reward decreasing morbidity and mortality.
The frequency with which nutritional defects are en-countered is not appreciated by many physicians. A casual walk through the wards or private rooms of any large hospital will attest the high incidence of nutritional problems. Malnutrition is usually obvious in the patient with cirrhosis of the liver, advanced pulmonary tuberculosis or chronic ulcerative colitis. It is recognized readily that maintenance of adequate nutrition is difficult during the recovery period after total gastrectomy or resection of the colon. It is perhaps less obvious that nutritional problems are common and of significant import in the patient with congestive heart failure, rheumatic fever, peptic ulcer or some type of allergic state. Similar examples could be cited in all branches of medicine.
In view of the frequency and importance of nutritional problems in medical practice, a review of the methods and procedures currently available for nutritional diagnosis and of criteria useful in the evaluation of nutritional status seems warranted. Nutritional diagnosis is not so exact that abnormalities of cellular chemistry can be detected with precision. Much remains to be learned and new tools and methods must be developed. Nevertheless, progress has been rapid. The present state of knowledge and areas requiring future development will be summarized in the sections that follow.