Body composition and muscle constituents during weight loss: Studies in obese patients following gastroplasty

Background: The influence of rapid and prolonged weight loss on body compos ition and muscle constituents in the obese patient is not well known. There are serious complications related to rapid and prolonged weight loss. It i s of general interest to increase the understanding of the mechanisms and c onsequences of significant weight loss in man. Methods: In 40 obese patients, the body composition and muscle constituents were studied before and during 1 year of weight loss following gastroplast y. The study was undertaken in two groups (A and B) of obese patients, comp rising 32 women and eight men, body weight 82-175 kg and aged 24-49 years. Mean BMI in group A and B was 45 (W/H-2) and 43 (W/H-2) respectively. Body composition was assessed by total body potassium measurements and muscle co nstituents were determined by analyses of muscle specimens obtained percuta neously. Results: The preoperative body composition was found to be equal parts of l ean body mass and body fat. Preoperatively, muscle constituents revealed a higher protein content per cell and a lower potassium concentration related to fat-free solids. The loss of 18-28% body fat and lean body mass occurre d in equal proportions during the first 3 postoperative months of rapid wei ght loss, followed by a continuous decrease of body fat but not of lean bod y mass. The concentrations of proteins and potassium per muscle cell reveal ed a reduction during the period of rapid weight loss. The RNA/DNA ratio 1 year after surgery was still reduced, indicating a low protein synthesis ra te. Conclusions: Preoperatively mean body fat accounted for 50% of the body wei ght in obese patients. Following weight loss, body fat, lean body mass and concentrations of proteins were reduced compared to preoperative values. Af ter the period of rapid weight loss, with reduction of lean body mass and b ody fat in parallel, a progressive reduction of body fat was observed where as the lean body mass did not decrease further. Protein synthesis rate was still low 12 months after surgery.