A really interesting web site on Trans Fats and how unhealthy they are. Update: site has gone away, but read more here.
I had previously read a lot about them in Dr. Atkin’s New Diet Revolution and also in The Okinawa Program. Both of them say essentially the same thing; that trans fats lower good cholesterol and raise bad cholesterol, and that they are not required to be listed on the the nutrition labels, so people have no idea how much of this stuff they’re consuming. Here’s a study from Harvard that explains pretty well what Trans Fats are and how they affect you.