The expression "sexual abuse" refers to an adult paying sexual attention to a minor. This can include different behaviour types, but are all put into effect through force, without the child's consent. The adult who abuses is bigger and stronger and usually has power and authority over the victim.
With this power they can force or corrupt the children by obliging them to submit to abuse.
There are people who have been sexually abused as children, and who do not have eating disorders. And there are people who have eating disorders, but who have not been sexually abused. So there is no direct relationship.
However, any kind of childhood trauma may contribute to eating disorders, for people who have an inclination towards eating disorders. If you have encountered traumatic episodes as a child, they can show themselves as different kinds of neurotic behaviour, including eating disorders. Data from scientific literature seems to show that the abuse undergone during childhood can indirectly affect psychological processes that predispose children to food pathology development.The physical or sexual abuse present in patients can sometimes make them more mistrustful of people who try to help them (including the therapist). This tends to make the therapeutic relationship more difficult.
Getting into contact with your suppressed memories and the feelings around them, can help you combat eating disorders.