The physiology of nutritional assessment and therapy in protein-calorie malnutrition

Protein-calorie malnutrition (PCM), in the purest sense, is the result of depleted body protein stores due to semistarvation. A review of the hormonal response to simple semistarvation illustrates the elegant adaptive ability of the body to respond to an inadequate diet. By contrast, the body's metabolic response to an injury or illness stimulus is a dynamic process orchestrated by monokines and hormones. Although the injury response, strictly speaking, is not synonymous with PCM, the resultant increased energy expenditure, anorexia, and potential for skeletal muscle breakdown can result in an even more rapid depletion of body protein stores. Ultimately, the need for nutritional support depends on the amount of recent weight loss, anticipated time of insufficient oral intake, and the degree of stress. A discussion of basic concepts of anthropometry precedes examples of advantages and disadvantages of a given anthropometric parameter for selected disease states. The effects of PCM on visceral structure and function are discussed in detail so that the reader can appreciate why the metabolic response to injury may have a very different impact on the nourished compared with the malnourished patient. Particular attention is paid to the adverse effects of PCM on immune function and its antithesis, the beneficial impact of nutritional repletion on the immune system. An approach to refeeding discusses indications for initiation of nutritional support, choice of route, design of a macronutrient and micronutrient regimen, and guidelines for monitoring. Familiarity with the metabolic alterations of refeeding is key to the mitigation of potentially life-threatening complications of sudden refeeding. Appreciation of the anticipated response to nutrition is important, as the response will vary with the degree of stress. A nearly optimal response can be expected with appropriate nutrition in the nonstressed semistarved patient, whereas inefficient repletion is to be expected in the severely stressed patient. The review concludes with a discussion of the role of nutrition as a modifier of the body's metabolic response to injury.