Principles of Nutrition
“Healthy” or “normal” BMI is defined numerically as 18.5 to 24.9. Values above and below this range are with increased health risks. Although BMI can be calculated with a mathematical formula, table and monograms are available for convenience (see Chapter 14). One drawback of using BMI is that a person can have a high BMI and still be undernourished in one or more nutrients if intake is unbalanced or nutritional needs are high and intake is inadequate.
Weight Change
Unintentional weight loss is a well-validated indicator of malnutrition (White et al., 2012). The significance of weight change is evaluated after the percentage of usual body weight lost in a given period of time is calculated (Box 1.3). Usually, weight changes are more reflective of chronic, not acute, changes in nutrition status. The patient’s weight can be unreliable or invalid due to hydration status. Edema, anasarca, fluid resuscitation, heart failure, and chronic liver or renal disease can falsely inflate weight.