Brittany and Richard Have Noticed That Their Friend Mandy Has

Brittany and Richard have noticed that their friend Mandy has lost a significant amount of weight over the course of the spring semester. People are starting to comment on how thin she looks. Brittany has noticed that Mandy eats an orange for breakfast, a small bowl of salad with no salad dressing and a small piece of grilled chicken for lunch, and a cup of plain yogurt for dinner. Richard has been going to the gym with Mandy most days of the week. He enjoys lifting free weights, and Mandy usually runs on the treadmill for 45 minutes and then does 15 minutes of core exercises.
In addition, Mandy has shared with Brittany that she has not had her period in four months. Mandy has also expressed that she is frustrated because people are making comments about how thin she looks and consequently has not gone to as many parties or social gatherings because she feels so uncomfortable.
Last week Mandy hurt her leg while running. The doctor said that Mandy has a stress fracture. Why might Mandy be prone to stress fractures?

A) She is most likely in an iron-deficient state.
B) She most likely has decreased bone mineral density.
C) She most likely developed lead poisoning.
D) She exercised too much.
E) She has low body fat.