DEAR HARRIETTE: A new friend of mine who is a fitness buff recently told me that when she was much younger, she was bulimic. She described the whole scenario of how she got caught up in this behavior when she was in college and how, eventually, she got past it. She looks healthy today, but I do know that she is an overexerciser. She used to run until her knees gave out. Now, she bikes nearly 30 mi…