Oils don't have to reach a smoke-temperature before they change their properties and become less healthy.
One of the reasons I switched to groundnut oil is that I heard an 'expert' suggest that, whilst it was not much more healthy than sunflower oil when cold, after heating sunflower oil becomes extremely bad for you.
We've all heard that monounsaturates are the best, poly- the next best and saturated the worst type of lipids; and groundnut oil lies midway between the healthier olive oil and the 'neutral' sunflower oil, but apparently the situation changes after the oils have been heated just once, and to quite a low temperature!
Apparently groundnut oil is the healthiest to cook with; sunflower oil, regarded as ambivilent when unheated becomes EXTREMELY bad for you after heating. Olive oil effects the taste of the curry.
I have used Rice bran oil too, but I excepting it's relatively benign properties when cold, I have no idea what it's like after it has been heated! I'd like more info on this!
Anyway the Misses and I stick to groundnut for curry and chinky, and olive oil for the Mediteranian stuff; which we think is a good compromise on taste v. health.
Low-fat food is SOOOO boring!