Your guests won't know the difference. All you have to do is substite high fat or calorie items with ones that are lower in calories or fat. You can whip it, use it in sauces, casseroles, and even the pumpkin pie. Applesauce fills in for oils in baked goods. Try equal amounts of it in muffins, breads, cakes, and cookies.
Fruit juice is a good base for salad dressing or marinade.
Cocoa powder is the chocoholics answer. Cocoa powder works in brownies, cakes and fudge, just use three tablespoons for every ounce of unsweetened chocolate.