Alterations in body composition after gastroplasty for morbid obesity.

Body compositional changes during rapid weight loss and after weight stabilization were prospectively studied in morbidly obese patients undergoing gastroplasty operations. Body composition was studied preoperatively and 6 and 24 months postoperatively in 23 patients by use of a total body counter (40K) and an isotope dilution technique. The mean fat mass, cell mass, and intracellular water (ICW) decreased during the first 6 months (p less than 0.001) and remained unchanged at the 24-month test. However, the mean liters of extracellular water (ECW) did not change. Consequently, the ECW/ICW ratio, high in states of malnutrition, rose above postoperative levels. A strong correlation was found between decreases in cell mass and increases in the ECW/ICW ratio.