This study aimed at a better understanding of the role of fitness sports in the development of eating disorders (ED) among women, using a dual—qualitative and quantitative—approach. A total of 1,270 participants responded to a questionnaire, and 25 women with clinical ED were interviewed. The results showed a total of 10.31% of fitness sport participants to be at risk of developing ED. The risk varied according to the commitment factors in a sport activity (i.e., location of activity, type of fitness classes, frequency and amount of practice). The role of fitness sports in ED was ambivalent, related to the variety of reasons for practicing them. These sports were sometimes used as a way of losing weight, sometimes in order to eat more, or to treat ED. Women suffering from ED primarily carried out free, individual, cardiovascular activities. Therefore, the prevention of ED in private fitness centers could primarily target group cardiovascular fitness classes, as well as participants in free cardiovascular activities.