As far as what specialty of nursing you want to go into when people ask you....don't feel like you have to pick anything at all right now! That's why you have all different clinical sites, to experience what's out there. I know that I thought for sure I would be in nursery or L&D, once I went to ICU I could not be dragged back to women's health. Most people take a few jobs before they settle into an area, and some people change areas throughout their career. Nursing is so versatile.
I think if you really wanted something fitness/nutrition related, you could still be an RN and then get another degree or certification. Check out the nursing electives your school offers. I know a person from nursing school
with her first bachelor's in exercise science, then went back for nusing. You could work in cardiac rehab as an RN and then you could help develop programs for the patients drawing on the exercise/nutrition part of it. An RN can practice independently. There is nothing wrong with an RN having an office or opening a fitness center and advising people within the limits of the scope of practice defined by the state. Check out http://www.independentrn.com/faqs.cfm
. You could work as a hospital nurse for a few years, fine tune your skills and make professional contacts while putting together an independent practice. Good luck!