The exchange of melted butter to the packet of liquid Butter Buds will be even. Don't bother with dietetic versions. When baking cakes or cookies, you can evenly exchange applesauce or pureed prunes with the butter or oil to reduce the fat. Don't feel that you have to add more sugar though to make up for the flavor. The fat replacement had more than enough flavor.
Low fat is a good way of reducing fat and calories, but stay away from fat free.