Impact of Denosumab in the Prevention of Bone Loss in Non-menopausal Women With Anorexia Nervosa

Inclusion criteria: * Patients with a current AN defined by DSM-V criteria * Being female * Age over or equal to 18 years and less or equal to 40 years . For patients under 20 years of age, effective bone maturation (attested by a radiography of the hip) * Agree to take contraception up to five months after the last injection of denosumab . * Absence of pregnancy evidenced by an interview and a negative assay of human chorionic gonadotropin (ßhCG). * Evidence of low BMD determined by Z-score value \< -2 DS (at least one site (lumbar spine or total proximal femur) * Signing an informed consent. Exclusion criteria: * Not affiliated to a social security scheme or not being the beneficiary of such a scheme. * Severe hepatic cytolysis with transaminase up to 5 times normal. * Severe dental problems: in case of doubt an assessment by a dentist will be required before inclusion. * Desire of pregnancy during the two years of follow-up study. * Disease or treatment potentially responsible for secondary osteoporosis. * Participant already treated with a molecule known to have an effect on bone * Diabetes. * Current hypocalcemia. * Immunodeficiency. * Cancer with bone lesions * Patient on protectice measures (guardianship or trusteeship) * Hypersensitivity to the active substance or to any of the excipients of Prolia® * Unable to read and / or write and understand the methodology of the study * Reporting relationship to the investigator * Anticipate a long stay outside the region that would prevent compliance with the schedule of visits * Participation to other biomedical research on health products * Deprived of liberty * Breastfeeding