Research has shown that eating disorders and depression often go together in girls and women. One study found that 46% of inpatients with bulimia also had depression. However, it is not known whether depression causes bulimia, bulimia causes depression or if the relationship works both ways. Researchers from Southern Methodist University in Dallas studied 496 adolescents over an eight-year period. They found that depression predicted bulimia and bulimia predicted depression i.e. the relationship worked both ways. However, the relationship was weak in both directions suggesting there might be a third factor behind the link.
Presnell, Katherine ... [et al] - Depression and eating pathology: prospective reciprocal relations in adolescents Clinical Psychology and Psychotherapy July-August 2009, 16(4), 357-365