Woohoo! Walt Disney World is my favorite vacation spot, and I've been there 9 times. The last time was last month.
There are healthy food choices at just about every Dis restaurant, offering salads, fruit, etc. I've lost weight while being at Dis, and didn't go hungry at all. One thing I did was to order the kids' portion. The adult portions are easily large enough for 2 people, so you could share with someone, if you'd rather go that route.
If you are staying on Disney property, the resort hotels have a deli section in the food courts, with many, many healthy choices for breakfast and lunch.
Here's a place where you can look up the menus at most Disney restaurants, at the resorts and in the parks:
http://www.allearsnet.com/din/dining.htm
That place has all the Disney info you could possibly want, not just dining info. Have fun, and tell Mickey I said hi.