When does a "healthy" habit turn into a problem?

CrossCurrents

According to Christine Courbasson, an eating disorders specialist at the Centre for Addiction and Mental Health, there is a fine line between being obsessed with body shape and having an eating or exercise disorder. Symptoms that an interest in fitness has become anorexia athletica include:

exercising over and above the requirements for good health
exercising despite physical illness or injury
linking exercise achievements with calories burned
exercising as a direct response to calories consumed
defining self-worth solely in terms of performance
repetitive, obsessional thoughts about weight and diet
compromising work, school, and relationships to find extra time for workouts
forgetting that physical activity can be fun
feeling compelled to push on to the next challenge
justifying excessive behaviour by insisting that the exercise is necessary or healthy