Here’s part two of my friend Brad’s primer about fat:
So then, you may ask, why is vegetable oil bad for me if it isn’t partially hydrogenated? The simple answer is oxidation. Double bonds are less stable than single bonds and therefore the more unsaturated an oil is, the more prone it is to oxidation. Oxidation of fats is bad.
If you want an example of oxidation, you can buy a bottle of flax seed oil. Flax seed is very high in highly unsaturated omega 3 fatty acids. If it is pressed at low temperatures, kept in a cool, dark place and not exposed to oxygen, small amounts of it are probably very good for you. If you take a bottle of it, open it up and leave it in front of a warm, sunny window, it will quickly turn into – linseed oil. Linseed oil is oxidized flaxseed oil and it is rank. It is used as a wood sealer. It is unpalatable.
But soybean oil also contains a fair amount of omega 3s and omega 6s, which are also prone to oxidation. That is why vegetable oils are high in antioxidants, particularly Vitamin E. In the plant, the vitamin prevents the oils from oxidizing.
The problems with vegetable oils start in the processing steps. I like to think about this problem with a question, “How DO you get oil out of corn??” (or soybeans) The answer is with high temperature hexane extraction. Hexane is an organic molecule used as a solvent and it is nasty stuff. It’ll melt off your skin. It’s also a known carcinogen. The reason they use hexane is that fat is soluble in
hexane, but not protein and water, so the oil ends up dissolved in the hexane. Then, they heat it up and the hexane boils off, leaving you with oil. What you learn in orgo (organic chemistry) is that the first law of organic extractions is that you never can get a 100% pure end product. Which means that there’s hexane in vegetable oil.
Another problem with the oil at this stage is that it’s been heated, so many of the antioxidants have been destroyed and the oil is rancid. And stinky. So they boil it with a nickel catalyst – another carcinogen – which removes the stench (at least a little). Then it is subjected to bleaching and several other treatments before they bottle it (or make Twinkies out if it) and sell it you, sometimes with a hydrogenation step.
Incidentally, the reason that olive oil is better than “vegetable oil” is that first of all, it is mostly monounsaturated and thus, it is much more stable. Second, it can be cold pressed with simple equipment, which doesn’t oxidize it, and the natural antioxidants are kept intact. It is therefore stable at room temperature for long periods. You still shouldn’t leave it in a warm sunny window, though.
But let’s say that we could extract vegetable oil in a non-solvent based manner. Would it be good for us then? Probably not, at least not in large amounts. One important health issue is that we should try to minimize the ratio of Omega 6 to Omega 3 oils in our diet. These oils are used in many hormone pathways and too much omega 6 screws these pathways up. The second reason is that, like I said before, you are what you eat. When you eat lots of omega 6s, they end up in your membranes. This can be seen in the cattle industry. When you take a cow off pasture and feed it soybeans, the Omega 6 to Omega 3 ratio in beef goes from like 3 to 10 or 20 in just a few weeks. And remember that they are easily oxidized. Now you have easily oxidized fats in your membranes – not good! In fact it has been theorized that a large reason for the increase in skin cancer this century could be due to the increasing amount of easily oxidized omega 6 in our skin cell membranes. Now when you walk into the sun bad things happen.
Finally, I think an interesting thing to note is that pork fat and olive oil are very similar in composition. Pork fat, according to the USDA, is 40% saturated, 45% monounsaturated and 11% polyunsaturated (it’s not clear to me why these numbers don’t add to 100). Also, pastured pigs are probably lower in polyunsaturates. Olive oil is 14% saturated, 74% monounsaturated and 8% polyunsaturated. Compare this with soybean oil, which is 14% saturated, 23% monounsaturated and 58% polyunsaturated. So when they say you should approximate a “Mediterranean Diet” and eat things like olive oil, if there’s no olive oil around, think, “Mmmmmm….. lard.”
OK, enough for now, gotta go to work, still haven’t talked about different length fats.