[Jensson]

Poly unsaturated fats easily becomes trans-fats when heated. This is very common in factory produced food since trans fats melt at higher temperatures making their shape easier to keep if you turn the poly unsaturated fats to trans fats.

But I don't think there are any dangers to poly unsaturated fats other than them easily turning into trans fats, so as long as factories are banned from making them into trans fats it should be fine. Or really the opposite, poly unsaturated fats are the healthiest fats, omega 3 and omega 6 and so on belongs to this group, just be sure to treat it carefully and don't let it turn to trans fats.

[bluGill]

There is one other problem with poly-unsaturated fats: they spoil fast - a few months at best at room temperatures. Since the crops are often harvested yearly and it takes time to get from field to market to your cupboard this is a real problem.

[feet]

Sounds to me like if you avoid heating them it's fine, which means there should be no issue with dietary PUFAs.

[Jensson]

Yeah, canola oil should be fine to use if you add it to food yourself. But as ingredients in fastfood or bread or chips it is likely they heated it enough to create trans fats.

[feet]

So the heating thing appears to be false. I wasn't able to locate literature in my brief search on the subject so perhaps someone can post a link