Mona is a 20-year-old student. mona is training to be a professional gymnast. she often restricts her diet to salads and fruit juices and trains 8 hours a day because she feels she needs to control her weight to perform well in competitions. she has noticed that her menstrual cycles have become irregular. on consulting a doctor, she is informed that her bone density is low. mona's symptoms indicate that she is mostly likely suffering from