Although there are advocates of both butter and margarine, most cardiologists agree that if you have heart disease or are at risk and you are following a diet for high cholesterol, certain types of margarine are better for your heart than butter.
Because margarine is made from vegetable oils, it contains no cholesterol. Butter is made from milk, which is an animal protein source, so it does contain cholesterol. Butter also contains saturated fat.
But all margarines are not created equal. Many types of margarine are made from hydrogenated vegetable oil, which means that they contain trans fats; exactly what you want to avoid on a low cholesterol diet.
Look for tub margarine rather than stick margarine. In general, the more solid the margarine is, the more trans fat it contains. Look for spreadable tub margarine with 3 grams or less of total fat, including both saturated fat and trans fat.
Are you a baker? Opt for butter. Not only is it heart-healthier in stick form than margarine, it gives your baked goods more flavor, which makes it easier to perform other low-fat substitutions in recipes. But that said, feel free to experiment. For example, try making a recipe with less butter than it calls for. You may be able to get away with a quarter cup rather than half a cup. Or substitute applesauce or prune puree for half or a third of the amount of butter when baking. (Caution: you many need to adjust the amount of dry ingredients to avoid over-wet batter).