Hydrogenated oils are evil...why?

In English, what affect do hydrogenated oils have on the body?

They tend to elevate LDL (bad) cholesterol, lower (HDL) good cholesterol, raise triglycerides, and promote atherosclerosis.

That’s a brief and oversimplified summary. Doubtless others will follow who have the time to elaborate more.

Hydrogenation is a process that changes unsaturated fats into saturated fats. It starts with an oil that’s high in mono- and polyunsaturated fats, which aren’t all that bad for you (they have less of an effect on ‘bad cholesterol’, less ability to cause atherosclerosis, etc.). Hydrogenation turns these oils into saturated fats. Saturated fats tend to be more solid at room temperature and have a longer shelf life. They have certain uses in manufacturing, but they tend to be more expensive than unsaturated fats because saturated fats usually come from animal sources. Hydrogenation is just a cheap way of making saturated fats from plant sources.

Vegetable oils are high in unsaturated fats, the better kind for your body. But hydrogenated vegetable oils are really saturated fats, the bad kind. Also, hydrogenated oils are the only source of trans fat. Trans fats are ones that are chemically not saturated, but have the same shape as saturated fats. Essentially, trans fats in your body act as if they were saturated fats, with all the associated health risks.

Of course, too much of any kind of fat isn’t healthy. If you eat a huge serving of fries cooked in only unsaturated fats, it’s still bad for you. Not as bad as if it was all saturated fat, but still bad. Finally, it doesn’t really matter if a food has zero trans fat if it’s high in fat anyway. ‘Zero trans fat’ is essentially the same claim as ‘no hydrogenated oils’. It says nothing about the actual saturated fat content. Remember that trans fats are just ‘unsaturated’ fats that do the same thing in your body as saturated fats, not some kind of scary poisonous fat.

Roches explained the differences brilliantly. For more information about hydrogenation, I thought the presentation at How Stuff Works was helpful.

I wish I could find a better reference than Men’s Health, but there have been some studies suggesting that trans fats promote muscle loss, which makes them a whole lot worse than saturated fats.

Also, IIRC, a small amount of saturated fat every day is actually good for your heart. The two are not quite the same.

Not quite true. As QtM said, trans fats not only raise LDL levels as all saturated fats do, but they also lower HDL levels, which normal saturated fats do not do.

In addition, “trans” fats are geometrically different from natural fats. Almost all naturally occurring unsaturated fats are in the “cis” formation. It is not unreasonable to think that cell membranes in our bodies that incorporate fats of an abnormal geometry might behave abnormally.

There is also evidence suggesting a link between trans fats and diseases that are not related to saturated fats in and of themselves, such as asthma and breast cancer. I’m not saying that these studies are definitive, but there is plenty of reason to be more cautious of trans fat consumption versus comsumption of a naturally-found saturated fat.

Related fat question:

Does cooking at high temperature affect the chemical make-up of unsaturated fats? I seem to recall hearing that cooking over and over with the same fats is a “bad thing” but that sounds kind of hokey to me.

mr_moonlight has already commented on your last sentence. I’d like to comment on the other sentences in that paragraph. Too much of anything is probably not a good idea, but there are healthy fats around, primarily the omega-3s and omega-6s: the short-chained omega 3 and the long-chain omega 3.
The long-chain Omega-3 fatty acids, the largest concentrations of which are found in fish, may lower the risk of heart disease and ease the pain of rheumatoid arthritis, by making blood less likely to coagulate and by suppressing a sequence of events that occurs between the cells of the immune system and those of the joints. (Health & Nutrition Letter, February 1999)

Polyunsaturated fatty acids are either “omega-3s” or “omega-6s.” Leafy greens and some vegetable oils (such as walnut, flaxseed, and canola) contain only the short-chain omega-3 linolenic acid, not the longer-chain fatty acids found in fish oils. Fish are able to convert the linolenic acid in algae and other sea plants into eicosapentenoic acid (EPA) and docosahexenoic acid (DHA). (U of Cal, Berkeley Wellness Letter, March 1999) Flaxseed, especially, has been touted as a good substitute for fish for obtaining EPA, but the body cannot readily convert that short-chain acid into EPA. Too much fish is probably not good for you, not because of the acids they contain but because of the mercury they may also contain.

Aren’t there omega-9 acids as well?

Yes, indeed. Oleic acid is omega-9. Disregard the silly site name and look here. It’s actually quite good. Omega-9, as applies to oleic acid (a monounsaturated fatty acid), is mentioned about 1/4 of the way down. The site actually informs the discussion in this thread. It’s straightforward and clear.

yes the amount of trans and oxidised oils goes up every time you cook with it.

Did anyone notice in the “How Stuff Works” link, how much those fatty acid molecules look like fuel hydrocarbons?

When I consider that a cupful of gasoline can move my car 10 miles and back, I begin to understand why it’s so hard to burn fat!

In case you overlooked it in KarlGauss’s cite, note the following:

Hence, one should try to obtain much more omega-3 than in the usual diet (about half as much as the omega-6).