On the Personalizer you can specify that you have certain dietary preferences or restrictions, but it is really not necessary because there are so many options. In the Horizon Court, there is always a salad bar and fresh fruit, (and cups of yogurt and a variety of cereal in the morning in addition to fruit). In the dining room, you can always ask for chicken or salmon prepared simply, such as broiled, if you don't see what you want on the menu, but there is actually a section on the menu with heart-healthy items listed for each course (they may even call it spa cuisine--I don't recall from last year how it was listed)! This is available breakfast, lunch and dinner in the dining room. In short, it should be no problem at all---they are very accomodating in the event you don't like the menu offerings or the Horizon Court. I always try to eat healthy, at least for breakfast, in the dining room and have never had a problem getting a half grapefruit and poached eggs or a healthy cereal. If seeing all of the food is too much of a temptation (they do walk around with trays of morning pastries, croissants and muffins!) you can always order just want you want through room service.
Hope this helps!