Why is partially hydrogenized soybbean or other oil bad for your health?

Not Polyunsaturated. With respect to the types of fat, polyunsaturated is better for you. A polyunsaturated molecule has more double bonds. When our body uses these fats to build inflammatory chemicals, these chemicals formed are less potent and cause less inflammation. When you hydrogenate them you are filling those double bonds and losing the benefits. It does make the fat thicker so it can spread like butter.