Fat mass protects hospitalized elderly persons against morbidity and mortality

Background: It is well established that the combination of protein-energy malnutrition and low body mass index (BMI) increases the risk of death in elderly patients, but recent studies indicate that the risk of death may decrease with higher body weight. However, these studies did not perform direct, separate, and reliable measurements of fat and lean mass by using a reference technique. Objective: Our objective was to evaluate the relation between body composition, based on the 4-compartment model, and morbidity and mortality in hospitalized elderly patients. Design: This prospective study enrolled 125 elderly patients evaluated at admission for body composition on the basis of BMI plus fat mass, lean mass, appendicular skeletal muscle mass, and body cell mass indexes (calculated as the ratio of the mass to the square of the height) measured by X-ray absorptiometry and bioelectrical impedance analysis. Outcomes were assessed 6 mo later by using a score system that takes into account complications (pressure ulcers and/or infections) and 6-mo mortality. Results: The fat mass index correlated positively (r = 0.19 and P = 0.023 adjusted for sex; r = 0.18 and P = 0.043 adjusted for sex, albuminemia, and C-reactive protein) with outcome score (1: death, 2: complications, 3: no complications). There was no significant correlation between outcome score and BMI, lean mass, appendicular skeletal muscle mass, and body cell mass indexes. Conclusions: This study clearly indicates that the generally accepted rule that overweight is associated with morbidity and mortality does not apply to hospitalized elderly patients, for whom fat mass is associated with a decreased risk of adverse events. Am J Clin Nutr 2009;90:505-10.