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Malnutrition can arise from primary or secondary causes, with the former resulting from inadequate or poor-quality food intake and the latter from diseases that alter food intake or nutrient requirements, metabolism, or absorption. Primary malnutrition occurs mainly in developing countries and under conditions of political unrest, war, or famine. Secondary malnutrition, the main form encountered in industrialized countries, was largely unrecognized until the early 1970s, when it was appreciated that persons with adequate food supplies can become malnourished as a result of acute or chronic diseases that alter nutrient intake or metabolism, particularly diseases that cause acute or chronic inflammation. Various studies have shown that protein-energy malnutrition (PEM) affects one-third to one-half of patients on general medical and surgical wards in teaching hospitals. The consistent finding that nutritional status influences patient prognosis underscores the importance of preventing, detecting, and treating malnutrition.

Definitions for forms of PEM are in flux. Traditionally, the two major types of PEM have been marasmus and kwashiorkor. These conditions are compared in Table 75-1. Marasmus has been considered the end result of a long-term deficit of dietary energy, whereas kwashiorkor has been understood to result from a protein-poor diet. Although the former concept remains essentially correct, evidence is accumulating that PEM syndromes are distinguished by two main features: dietary intake and underlying inflammatory processes. Energy-poor diets with minimal inflammation cause gradual erosion of body mass, resulting in classic marasmus. By contrast, inflammation from acute illnesses such as injury or sepsis and chronic illnesses such as cancer, lung or heart disease, and HIV can erode lean body mass even in the presence of relatively sufficient dietary intake, leading to a kwashiorkor-like state. Quite often, inflammatory illnesses impair appetite and dietary intake, producing combinations of the two.

Table 75-1 Comparison of Marasmus/Cachexia and Kwashiorkor/Protein-Calorie Malnutrition

An international consensus committee has proposed the following revised definitions. ...

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