This article presents research completed on eating disorders. First of all, symptom changes from eating disorders are shown with over time. Secondly, it takes a general view of epidemiology in eating disorders and realities at the present time. Thirdly, it takes a general view of the research on the appearance of diseases on subjects with eating disorders. The appearance of disease factor is divided into preparation and causal factors. In addition, the preparation factors are divided into the following three areas: 1. Social and cultural factors about a society that admires thinness (thin people) and the satiation periods with foods, etc. 2. Environmental factors within family relations, etc. 3. Personal factors such as perfectionism, threatening personalities, etc. Fourthly, the main four factors are described along with the assessment of the eating disorder. Fifthly, it shows a general view in a case study on eating disorders with each point discussed and a new treatment theory described. Finally, it discusses the necessity of this research from the viewpoint of why people have eating disorders and future problems in research.