As I understand, there is some *natural* trans fats (spiral turned the
other direction than in sis fats, that are the moust usual ones) in
bovine fat, also in butter. But these trans fats are "known" by the
body, so they might not harm in the same way.
There was a big research on 30000 american nurses two years ago or so,
that clearly showed that trans fats are 6 times (if I remember right)
more dangerous for resulting heart diseases than saturated sis fats,
which in turn were like 2 time as dangerous as not saturated fats.
But the (american) margarine industry were very quick to send a comment
to the news agencies pointing out the the researched ones more showed
that saturated fats a dangerous, thus hiding the problem with the
trans fats. I think people in genereal are not aware of the existence
of trans fats, and, at least here in Sweden, but probably in most countries
if not all, you are not obliged to tell anything about the trans fat
content of a food product.

- Hans