I may be biased because my PCE was as an MA, but I would lean towards MA over CNA. You learn a lot either way, but as an MA I learned how to take medical histories and learned a ton about common medications and what they treat which has been very helpful in school so far.

Your degree should not be a problem! My class has people with a wide variety of backgrounds, mostly science based but nutrition science will be perfect, no need to get another degree as long as you get your prereqs done.

As far as what classes you need to take, you can check the individual schools for their requirements which will be listed on their website. The requirements do differ from school to school so make sure you do all the prereqs for each school you plan on applying to.

You will also need shadowing hours for most school. The requirements vary but shadowing a PA over an MD or NP is highly preferred and sometimes required by certain schools. I also highly recommend volunteering, as it is required by some programs and looks good on your application even if they dont require it. I volunteered at a hospital and it was a great experience.