Margarine is not a suitable substitute for anything, except maybe WD-40. The process of hydrogenation, which makes the oils solid, creates trans-fatty acids , which are considered more unhealthy than the fats found in buttah. If you're scared about the fat in butter, use less or use vegetable oil. If you're a vegetarian, make an exception for butter or just use oil. Reader Jack Rosen points out that clarified butter, or ghee , is another lower-fat alternative to butter.
Ghee is easy to make, but easy to screw up and burn, too.
The sound will die down and return again after a minute or two. When it returns, remove the melted butter from heat and strain immediately through at least four layers of cheesecloth. A golden brown residue should be left behind. This is the milk solids that you worked so hard to get rid of. Refrigerate the ghee immediately.