Body Composition and Muscle Constituents During Weight Loss: Studies in obese patients following gastroplasty
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Background: The influence of rapid and prolonged weight loss on body composition and muscle constituents in the obese patient is not well known. There are serious complications related to rapid and prolonged weight loss. It is of general interest to increase the understanding of the mechanisms and consequences 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 gastroplasty. The study was undertaken in two groups (A and B) of obese patients, comprising 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/H2) and 43 (W/H2) respectively. Body composition was assessed by total body potassium measurements and muscle constituents were determined by analyses of muscle specimens obtained percutaneously. Results: The preoperative body composition was found to be equal parts of lean 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 occurred in equal proportions during the first 3 post-operative months of rapid weight loss, followed by a continuous decrease of body fat but not of lean body mass.The concentrations of proteins and potassium per muscle cell revealed 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 rate. Conclusions: Preoperatively mean body fat accounted for 50% of the body weight in obese patients. Following weight loss, body fat, lean body mass and concentrations of proteins were reduced compared to preoperative values. After the period of rapid weight loss, with reduction of lean body mass and body fat in parallel, a progressive reduction of body fat was observed whereas the lean body mass did not decrease further. Protein synthesis rate was still low 12 months after surgery.
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