Oil and Heat

Since there are several good books that discuss the impact of different fats on health and body composition, I'll avoid a detailed discussion of fats in general and focus simply on giving you a quick overview of what heating does to fats.Heating, under both normal high-temperature household conditions (pan frying) as well as more extreme conditions (repeated deep frying), affects both the characteristics and composition of dietary fat. Heating changes the chemical structure of the fat and leads to oxidation as well as the loss of some nutrients like antioxidants and essential fatty acids. These changes are relatively universal and only vary in degree (pun intended) and duration of heating.
All oils will oxidize in a big way if repeatedly heated to high temperatures for long periods of time. But even normal household frying temperatures and durations can cause partial oxidation. Some fats, however, do better than others. Saturated fats like butter and tropical fats like coconut and palm oil are the most resistant to oxidation since they're more heat stables.Olive oil (due to its phenolic content and monounsaturated structure) is next in terms of resistance to oxidation and heat stability. Olive oil can be made more stable by the addition of antioxidants to the oil (for example, Vitamin E). And polyunsaturated fats bring up the rear as the most easily oxidized fats and the least stable.Therefore we now have an order of "cooking safety,” showing that the saturated fats were the best while olive oil and polyunsaturated fats are the worst. This means that the physio-chemical properties of the good, "healthful" oils are the worst with cooking. Therefore the picture emerging is that the "good fats" need to be unprocessed and unheated in order to stay "good."
Although I hate to do this to you, there's more bad news for us to contend with. While there are big increases in lipid oxidation products with heated oils like olive and safflower, there are also measurable physiological effects as a result. Cooking with these oils also leads to increases in plasma triglycerides and LDL cholesterol (the bad kind) and decreases in HDL cholesterol (the good kind) when compared to non-heated oils (which actually do the opposite). So not only does heating affect the fat, but it affects how the body handles the fat. Strike two!
Finally, I'll give you the last piece of bad news. It's well known that pan-frying/grilling meat will typically produce mutagenic (cancer-causing) agents. However, newer data are showing that cooking with most oil actually increases the heat transfer from the pan to the meat, increasing the mutagenic activity of the food. Strike three!
So, with all of this bad news, what's a health conscious person to do? Well, I'm about to make some recommendations. Keep in mind that some of them may go against conventional thought and/or practice. But this section is not here to appease the masses.

The following recommendations will optimize your use of fats for both health and physique enhancement. Never use additional fats when pan-frying/grilling meat! If pan-frying/grilling meat use a non-stick surface or coat the pan with a minimal amount of some sort of cooking sprays. This will prevent large increases in the amount of mutagenic chemicals formed.
Never use mono- or poly-unsaturated fats when pan-frying! When pan-frying non-meat dishes use a non-stick surface or coat the pan with a minimal amount of cooking spray. If some sort of oil must be used for this type of cooking, use a saturated fat source like butter since these types of fats are most stable. Just be careful with how often you do this since excess saturated fat intake presents a whole other host of health problems.When baking, use saturated fats and/or olive oil only! These are best to use for oil stability reasons (but see above for saturated fat warning).
Never heat flax oil or fish oil! Oil supplements like flax oil and fish oil need to be consumed without any further processing or else their EFA (essential fatty acids) content will be destroyed. Exposure to heat and light should be prevented. In addition, olive oil is best when the extra virgin type is consumed and it's consumed unheated. Corn, canola, safflower, flax, etc. oils are the least heat stable of the oils, will become highly oxidized, and will lose their EFA content with cooking.Never, ever deep fry foods!Never, ever cook with polyunsaturated fats!