Any route for getting a "dietitian" degree?

Go back to college. Go to colleboard.com and check out the Universities in your area, there are links from collegeboard to the University websites. On the University websites you can see what majors are offered and what classes are required, you may be able to use a lot of the courses you have already taken to get your business degree like English and history.

you would need a degree in nutrition (or foods and nutrition, or dietician... it sometimes goes by different names) since you already have a degree, you would probably be exempted from taking most of the core classes - some of the business courses may even be requirements for the degree, but you'd have to see what the major requirements are.