Map of life expectancy at birth from Global Education Project.

Tuesday, September 12, 2006

No excuse

I've addressed the trans fat issue briefly before, but it deserves a post of its own. I assume that most of my readers already know that trans fats are bad for you and that they are basically unnatural. It would be very easy to remove 80% or more of trans fats from the American food supply, and according to an estimate by Mozafarrian, et al (NEJM, 354(15), 13 April, 2006) doing so would reduce heart attacks and deaths from coronary artery disease by about 12% (more or less).

Fatty acids are hydrocarbon chains terminating in a carboxyl group (COOH). If you remember your high school chemistry you know that carbon has a valence of 4, so carbon atoms in chains can have single bonds with the carbons before and after, and two hydrogen atoms attached; or a double bond with one of their neighbors and one hydrogen atom attached. If the hydrogen atoms on each side of the double bond are on the same side of the chain, that's called the Cis configuration; if they are on opposite sides, that's called the Trans configuration. Fats with no missing hydrogen atoms, and no double carbon bonds, are called saturated fats.

Most animal fats are saturated, most vegetable oils are unsaturated. All unsaturated vegetable oils are Cis fats. Trans fats are rare in animals as well, though bacteria in the guts of ruminants produce small amounts of trans fats which end up in milk and meat. Everybody knows that eating a lot of animal fat -- meat and dairy -- raises your level of "bad" cholesterol (Low Density Lipoprotein) and so increases your risk of heart attacks and strokes. So, you should eat vegetable oil and particularly monounsaturated fats (i.e., one double carbon bond) such as olive oil, and stay away from animal fat, although a little is okay.

Now, you'll note that animal fats are generally solid at room temperature. That's because the saturated fatty acid chains are straight. They lie next to each other, tightly packed, and form a solid or at least a buttery glob. Vegetable fats, however, bend at the Cis bond. Therefore they can't pack tightly, they slide past each other, and you have liquids such as a beautiful silky olive oil. Industrial "food" manufacturers discovered that they could add hydrogen atoms to polyunsaturated vegetable oils by heating them in the presence of steam. In the process, the remaining Cis bonds are transformed to Trans bonds. As a result, the chains straighten out and the fats become semi-solid. The manufacturers like these kinds of fats because they don't turn rancid easily, they hold up well to the high heat of deep frying, and since they are semi-solid they can be used as shortening in crackers and packaged cakes and so on.

So now they are ubiquitous in the American diet. While dairy and meat fats may be 1 to 8% Trans fats, in french fries and other deep fried fast foods Trans fats are 25% or more of total fats. And those "healthy" granola bars? 18%. In crackers, the number is 34%. Doughnuts 25%, cookies 25%. Etc. (Mozaffarian et al)

So what does that do to you? Not only do trans fats raise levels of LDL, unlike saturated fat they also lower levels of the "good" HDL cholesterol. And they raises the levels of triglycerides, and cause other changes in blood lipids that raise the risk of heart disease and stroke. There is also evidence that they promote inflammation, further raising the risk of heart disease and diabetes. There are numerous other less well established harmful effects of trans fats.

Now, here's the bottom line: there is no health benefit from consuming trans fats, unless you count the empty calories they provide. On the other hand, they are very nasty poisons. They kill you the hard way.

Unfortunately, although manufacturers are now required to list Trans fats on food labels, if the specified serving contains less than 500 milligrams, they can give the amount as "zero," i.e., they can lie. Which they do, with glee. If you eat several cookies or a couple of handfuls of potato chips, you may consume several grams of Trans fats, even though the label says "zero trans fats." If you read the label more carefully, and see that "partially hydrogenated vegetable oils" are listed among the ingredients, you know that the "zero trans fats" claim is a lie, and you should avoid the product. However, that won't do you any good in restaurants.

Denmark has outlawed the sale of foods containing more than 2% artificially produced trans fats, which pretty much eliminated them from the food supply. Manufacturers were able to substitute Cis fats, and some saturated fats from palm oils, which are not good but better than Trans fats. Nobody noticed the difference. If you order your Freedom Fries or Chicken McNuggets in a McDonald's in Denmark, you will eat zero Trans fats, and they will taste exactly the same. (Which is still a good reason not to eat them). Other than that, nothing bad happened.

We don't even need legislation. The FDA could decide that Trans fats are no longer "generally regarded as safe," which would largely eliminate them. Don't hold your breath.

1 comment:

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