My sister is a dietitian, and I would recommend a dietitian over a nutritionist, because a dietician has to have a degree and a nutritionist's credentials can be iffy.
When I was in college, I went to a few sessions with a dietitian. It was a hospital-college collaberative program and you got two or three sessions free, and then had to pay if you wanted to continue. I only took the free sessions, and the advice was good, but rather "generic" (nothing I didn't already know, just needed to put into practice). I really did love the nutritional analysis they did though. You had to keep a journal of everything you ate for one week. Then the dietitian did an analysis of your best day, your worst day, and your overall nutrition.