Use any other natural fat or extra virgin cold-pressed oil. Do not use margarine or processed oils. u003cbr/u003eu003cbr/u003eThey are nasty for your healthy and terrible for mashed potatoes. Try some good olive oil instead of butter. u003cbr/u003eu003cbr/u003eIt lightens the dish a bit and adds lots of healthy fats butter lacks. Just take note that it will not be as luxurious and creamy.