Since butter is all fat, I should eat margarine instead of butter right?

Probably not. Both margarine and butter are all fat but they are different types of fats. For a long time, people thought margarine was better because it was made from corn oil and not saturated dairy fat like butter. However, corn oil in its natural state is a liquid. To make it into margarine, which is solid (like butter) at room temperature, the liquid oil is infused with hydrogen making margarine a trans-fat sometimes known as hydrogenated oil. Trans fats have been found to increase LDL cholesterol (the bad form) and decrease HDL cholesterol (the good form). While the saturated fat in butter raises LDL, it does not negatively affect HDL. Saturated fats from animal and vegetable sources provide a concentrated source of energy in the diet; they also provide the building blocks for cell membranes and a variety of hormones and hormone like substances. According to information from the FDA, removing all trans fats from food would prevent approximately 7,000 heart attacks each year. A few margarine products are now available that claim to be free of trans fats. If you use margarine make sure you choose one that is free of trans fats.