Weight loss and body composition

Body fat accounts for much of the excess weight in obese persons; but the amount of lean body tissue (muscle and other protein tissue) in the obese individual is similar to that found in the normal individual. In weight loss primarily excess fat should be lost; not essential protein tissue. Complete fasting has been proposed as a technique for losing weight, in lieu of partial caloric restriction. The present studies were carried out to evaluate these techniques for weight loss. Changes in body composition of obese rats were determined after the animals lost one third of their body weight on different regimens. Obese animals which were restricted to 37.5 and 60% of ad libitum caloric intakes required 53 and 93 days, respectively, to lose this weight, whereas those which were totally fasted required only 24 days. There were significant differences in body composition of these groups after weight loss. Fasted animals lost more protein and less fat than did animals restricted in caloric intake; the fasted animals lost 18% of their total body protein, whereas the calorically restricted animals lost only 8舑9%. Epididymal fat pads were twice as large in the fasted animals as in the calorically restricted animals. In fasted animals, liver weight loss was greater than in restricted animals, but liver fat levels were still high, as in the obese rats. Liver cholesterol levels were also elevated in fasted animals. Neither the amount of fat nor the type of fat (unsaturation) in the diet had any significant effect on the rate of weight loss or on gross body composition. Type of fat affected fatty acid composition of plasma, but not of liver or depot fat. The development of new methods for determining body composition in man has permitted reasonably accurate estimates of the amount of excess body fat in obese individuals. In obese subjects who lost weight on restricted caloric intakes of an otherwise nutritionally complete diet, most of the weight loss was as body fat, without significant loss of lean body tissue. The studies in man confirm the findings in animals. The extra weight in obesity is mainly fat, with very little protein and some water; when weight is lost by restricted intake of a good diet, the composition of the tissue burned is quite similar to that comprising the extra weight. Fasting gives more rapid weight loss, but apparently less favorable changes in body composition.