It is widely known that it is easy to increase weight by changes in diet and lifestyle in Japan at present. The purpose of this study is to define "reducing body weight" as a diet and to examine in which part of body composition the effect of the 7-week diet program appears. The participants were women from 20s to 70years old who wish to perform a diet, and those who do not interfere with exercise training program. The implementation period was seven weeks from December 2010 to April 2016, and the number of times of physical training during the period was not specified, and it was set as the free will of the individual. The effect of the 7-week diet program conducted in this study was a significant decrease in average body weight. The weight loss can be predicted from the results of the regression analysis, and the effect of body weight loss appeared in decreasing body fat percentage and muscle mass regardless of age and BMI distribution. The areas where the greatest decrease occurred were the abdominal girth and thigh. These results suggested that continuing to do physical training and meal management from now on is expected not only for maintaining beauty and body form but also for prevention of muscle weakness and lifestyle related diseases.