This is a term coined by Peggy Claude-Pierre. It is the idea that all eating disorders have behind them a negative force, which causes the sufferer to feel worthless. In the case of eating disorders, punishment is adminstered through starvation or purging. It is also often closely linked to self-injury. They have been heavily criticised in the media for giving misleading information about weight loss.
Diuretic abuse is another method of purging.
Associated with both anorexia and bulimia, exercising is a way of purging the body of calories by burning them off rapidly. Many of those with an eating disorder exercise in secret, so that they don't arouse suspicion. This is extremely common and is one method of treatment. Nowadays, it usually involves a combination of physical and pyschological therapy. This will have the aim of getting the individual up to a safe weight and also giving them psychiatric help.