The Japan Society for the Study of Obesity recommends a weight loss of 3% of body weight over a period of 3-6 months. However, the effects of rapid weight loss on the body composition have not yet been adequately studied. Therefore, we observed the changes in the body composition induced by rapid weight loss and its effects on the pathophysiological mechanisms involved in obesity. The subjects were people with obesity admitted to our institution. The goal was to achieve a 3-5% body weight loss in the subjects by combining a carbohydrate-controlled therapeutic diet of 25-30 kcal/day per kg target body weight, exercise therapy, and pharmacotherapy. The body composition was measured at admission and at discharge by the dual bioelectrical impedance analysis. After 2 weeks, the participants' body weight decreased by 4.2%
the visceral fat area decreased by 16.7%, the subcutaneous fat area by 2.4%, and the lean area by 4.0%. The moderate weight loss, moderate energy restriction and adequate protein intake significantly reduced the visceral fat area while allowing the lean area to be preserved. Improvements were also noted in the peripheral white blood cell count and C-reactive protein level. However, no statistically significant changes in homeostasis model assessment for insulin resistance and the adiponectin level were noted. Regarding clinical parameters, improvements of the systolic and diastolic blood pressures, fasting plasma glucose, triglycerides, low-density lipoprotein cholesterol, and degree of microalbuminuria were observed. Short-term comprehensive treatment produced beneficial body composition changes, and improvements in the pathophysiological mechanisms involved in obesity.