Why is margarine bad for people?

Margarine is made by starting with oil and "partially hydrogenating" it, adding hydrogen bonds between the long chain oil molecules to make it solidify. This results in what are called "trans fats". The problem is that when you are making cells, if there are trans fats in your blood stream, the trans fats will be used preferentially when building the cell wall. As you are always building cells, you will end up with a certain amount of trans fats in the cell, which don't work as well as teh fats that the cell wall is supposed to have. The result is that the cells are weaker, making you more susceptible to disease, among other things. This is why many places are now outlawing the use of trans fats in commercial cooking.