Trans fats are unsaturated fatty acids (often cottonseed or soybean oil) that undergo a hydrogenation process to make them appear like saturated fat.
Some examples of trans fats include vegetable shortening and margarine, which are both solid in texture.
Initially, researchers saw potential benefits from this hydrogenation process such as better shelf-life and more stability at high heat. However, the problem is that these artificial fats were so different from anything in nature that our body did not know what to do with them.