It is often the case that people living with eating disorders can change their behaviour and symptoms to cross from one classification to another, for example, someone who has been bingeing and vomiting, typically associated with bulimia can begin to restrict the amount they eat or purge so regularly that their body retains little or no nutrients, causing them to rapidly lose weight more typical of anorexia.

While some people may cross various types of eating disorder, others may never fit neatly into any classification at all. Those in this category are usually diagnosed as having an Eating Disorder Not Otherwise Specified (EDNOS). People with EDNOS type disorders may show no clear pattern of eating behaviour but may still have obsessive thoughts about food and engage in behaviour which is detrimental to their health coupled with other psychological symptoms such as low self-esteem and depressive type thoughts.