Why is premorbid BMI consistently elevated in clinical samples, but not in risk factor samples, of individuals with eating disorders?

Body image disturbance is widely viewed as contributing to the development and maintenance of disordered eating. Yet this perspective is not inconsistent with the possibility that elevated premorbid BMIs also increase the risk of developing eating disorders. Research examining whether actual body size may play a role in eating disorder development reveals a curious pattern of findings. Few prospective risk factor studies conducted with community-based samples found a relationship between premorbid BMI and subsequent eating disorder pathology whereas retrospective research conducted with clinical samples indicates a consistent pattern of elevated premorbid BMIs relative to population norms or control groups. This study documents these disparate findings, considers potential explanations for them and proposes further study of premorbid BMI as a factor contributing to the psychopathology of eating disorders, particularly among those who come to the attention of treatment providers.