Nutritional health is maintained by a state of equilibrium in which nutrient intake and requirements balance. Malnutrition occurs when net nutrient intake (nutrient intake corrected for abnormally large fecal or urinary losses) is less than requirements. Malnutrition leads to a succession of metabolic abnormalities, physiologic changes, reduced organ and tissue function, and loss of body mass. Concurrent stress, such as trauma, sepsis, inflammation, and burns, accelerates loss of tissue mass and function. Ultimately, critical loss of body mass and function occur resulting in death (Figure 1).

The evaluation of the nutritional status is a broad topic, and to be of clinical importance, the ideal method should be able to predict whether the individual would have increased morbidity and mortality in the absence of nutritional support. In short, can the evaluation predict the occurrence of nutrition-associated complications (NAC) and thus predict outcome. Disease and nutrition interact so that disease, in turn, may cause secondary malnutrition, or malnutrition may adversely influence the underlying disease. Thus, patient outcomes are multifactorial, and attempting to formulate the influence of malnutrition on outcome based on single parameters or simple models fails to consider the many interacting factors. This complexity has been recognized in the recommendations of the American Dietetic Association.<sup>1 ADA's definition for nutrition screening and assessment J Am Diet Assoc 1994 ;  94 : 838-839

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Traditional nutritional science was first developed in the field of agriculture, where the effect of nutrition was entirely judged by the amount of meat on the carcass of animals and the production of proteins by the liver. This approach was embodied in the initial attempts to assess nutritional status in humans as given later under traditional nutritional assessment indices. These techniques lacked the ability to predict outcome and to detect early changes in function that occur with nutritional support. This article discusses some of the traditional nutritional assessment indices, then more recent assessment methods are evaluated with a view to: