I once heard that we shouldn't cook with olive oil, because the heat breaks it down into "bad stuff". I found this curious, since there is so much hype surrounding olive oil. So, naturally, I had to google to find out for sure. First, let me explain in simple terms why it matters which oil you use.
Every oil has what is called a smoke point. This is how hot an oil can get before it starts smoking. Once it starts smoking it breaks down, leaving a depletion of nutrients and the building up of harmful oxygen radicals, which are known to cause cancer. Yikes. Not good. Thus, it is important to know the smoke point of the oil you intend to use.
I personally have begun using grapeseed oil, since it has a high smoke point of 485 degrees F and is an excellent source of vitamin E. As for the olive oil inquiry? Well, you should be okay in most instances, though I did read that this issue is widely debated because it depends upon how the oil is processed and whether or not it is refined, etc. Below is a chart of smoking points, copied exactly from its source, GoodEatsFanPage.com.
200's 225 F: Canola Oil, Unrefined : Flaxseed Oil, Unrefined : Safflower Oil, Unrefined : Sunflower Oil, Unrefined 300's 320 F: Corn Oil, Unrefined : High-Oleic Sunflower Oil, Unrefined : Olive Oil, Unrefined : Peanut Oil, Unrefined : Safflower Oil, Semi-Refined : Soy Oil, Unrefined : Walnut Oil, Unrefined
325 F: Shortening, Emulsified Vegetable†
330 F: Hemp Seed Oil¥¥
350 F: Butter (Good Eats) : Canola Oil, Semi-Refined : Coconut Oil† : Sesame Oil, Unrefined : Soy Oil, Semi-Refined 356-370 F: Vegetable Shortening 361-401 F: Lard 375 F: Olive Oil (Good Eats) 389 F: Macadamia Nut Oil†† 400's 400 F: Canola Oil, Refined : Walnut Oil, Semi-Refined 406 F: Olive Oil, Extra Virgin* 410 F: Corn Oil (Good Eats) : Sesame Oil** 420 F: Cottonseed Oil† : Grapeseed Oil¥ : Olive Oil, Virgin** 430 F: Almond Oil*** : Hazelnut Oil*** 435 F: Canola Oil (Good Eats) 438 F: Olive Oil* : Rapeseed Oil*** 440 F: Peanut Oil† : Sunflower Oil† 450 F: Corn Oil, Refined : High-Oleic Sunflower Oil, Refined : Peanut Oil, Refined (Good Eats) : Safflower Oil, Ref. (Good Eats) : Sesame Oil, Semi-Refined : Soy Oil, Refined : Sunflower Oil, Semi-Refined 460 F: Olive Pomace Oil** 468 F: Olive Oil, Extra Light* 485 F: Grapeseed Oil** 495 F: Soy Bean Oil† 500's 510 F: Safflower Oil† 520 F: Avocado Oil, Refined
I hope this helps with your next stir-fry.