Course in nutrition can be run by anyone, and some are not worth the paper that are written on. Nutritionist is not a protected term, so some people call themselves that and give out whatever crackpot advice they like. So make sure you check that the course is properly recognised before you sign up! If in doubt check on here.
If you want to be a dietician then it is a degree course.
I have always been interested in Nutrition and Healthy Eating (don't necessarily practice it ) and for many complex reasons would like to study the subject 'properly' (but not really with a view to employment in the field - though you never know.