Don't rule out ordering food from gardengrocer and having it delivered to your room. We stay in a villa, so we have a full kitchen to store it all, but even in a regular hotel room you could stash some healthy breakfast and snack options.
I can tell you this: In my opinion it is difficult to eat "healthfully" at WDW - at least if you're trying to eat food that tastes good. The first year we went, I tried several "healthy" options at the counter service meals, and had lousy results. Much of it was close to inedible. The second time we went, I said, "To heck with it!" and ate what we like to refer as "bar food." Pizza, chicken strips, french fries, you get the picture. And that food tasted good. We really only ate lunch at the parks, though, and ate breakfast and most dinners at the villa, so eating one fried meal a day wasn't too bad.
The table service meals we've had at the more upscale restaurants, of course, have much healthier and tastier options. Good salads, fish, grilled chicken, veggies, etc.
Granted, our "yucky healthy food" encounters were 18 months ago - perhaps they have improved over time. Just my opinion, for what it's worth.