I am a Disney pro as we go there about 2-3 times/year!!!!! Check the forums at
www.disboards.com to see if others have posted comments about this topic as well.
But...Disney will help out anyone with food "issues", allergies or special requests. If you are eating at a sit down resturant (in all parks or hotels) tell your server that you have dietary needs and they will prepare your foods for you as needed (no sauces, no oils, egg whites, etc...). Eating at the buffets or counter service meals will be a little tougher but most if not all of them have lower fat items such as grilled chicken sandwiches (skip the bun if needed), salads, apples, carrot sticks, milk or water.
I suggest packing some protein bars to eat too for snacks so when you are at the park you don't get caught up in Mickey ice cream bars or popcorn! Also...the Kelloggs H2O protien poweder packs (like the crystal light packs) that you add to a bottle of water is a great option as it gives water more flavor but unlike crystal light it gives you 5 grams of protien to help you feel a little full while you are getting hydrated!
A lot of the snack stand in the parks now have fresh fruit or veggie sticks as a snack option which is great for those that want a healthier option!
Good luck and make sure you post when you are back to fill us all in on your Disney food experience!