The Skinny on Fats
By Robert L. Wolke, The Washington Post

One of the most bizarre phenomena in the world of publishing is the extraordinary success of books purportedly written for dummies and idiots. Readers apparently aren't the least bit insulted by being so labeled.

I have been thinking that maybe I should try the dummy-and-idiot technique in my writing, despite the fact that I am privileged to have the most astute readers any writer could wish for.

But there is one topic that has been crying out for such treatment, because the public has not been able to grasp it in any other way. I mean the topic of fats, where mass mystification still reigns.

So I hereby offer a sugar coated, deliberately oversimplified explanation "for dummies." May the gods of chemistry and pedagogy forgive me.

Shape Matters

Like people, different molecules have different shapes. What distinguishes one biochemical molecule from another is mostly its shape. Chemical reactions occur when the molecules collide. Then they either stick together like jigsaw pieces or break into new shapes. And there you have it: the shortest chemistry course in history. I'm going to explain all those fatty words in terms of the molecules' different shapes, because that's what makes them behave differently in our bodies.

FAT A fat is a particular type of chemical compound. Its molecules are shaped like a short flagpole with three long, starched streamers or pennants flying from it. The shapes of fat molecules -- and hence their properties -- differ from one another because the streamers themselves are different shapes. The flagpoles don't count.

What we popularly refer to as "a fat" in our diets, such as butter or vegetable oil, is actually a mixture of many kinds of fats. FATTY ACID Those three streamers flying from the flagpole are fatty acids (FAs): long chains of carbon atoms with a couple of oxygen atoms at one end, tying them to the pole. Our bodies' metabolism breaks off the FA streamers, which are absorbed. Their exact shapes are what determine their healthfulness. Common FAs include oleic acid, the primary FA in olive oil, and stearic acid, found in animal fats.

SATURATED FATTY ACID A saturated FA is one whose molecules are relatively straight. Saturated FAs are unhealthful because they raise the amounts of LDL ("bad") cholesterol in our bloodstreams. They are found mostly in animal fats. Butyric acid is a saturated FA found in milk fat (butter).

UNSATURATED FATTY ACID An unsaturated FA is one whose molecules contain one or more sharp bends or kinks. If an unsaturated FA contains only one kink, it is said to be monounsaturated; if more than one, polyunsaturated. Unsaturated FAs are found mostly in vegetable oils. They do not raise cholesterol levels. Monounsaturated FAs are even considered healthful. Olive oil's oleic acid is a monounsaturated FA.

OMEGA-3 and OMEGA-6 FATTY ACIDS These are polyunsaturated FAs that have kinks in their chains at either the third or the sixth carbon atom from the end. Examples are alpha-linolenic acid, an omega-3 FA and linoleic acid, an omega-6 FA.

Omega-3 and omega-6 FAs are "essential" FAs because our bodies can't produce them. We have to get them from our foods, such as fish oils, walnut oil, flaxseed oil and canola oil. Omega-3 FAs actually reduce our risk of coronary disease.

HYDROGENATION is a high- temperature, high-pressure process that changes kinky, unsaturated FAs into straight-chain saturated FAs, by forcing a pair of hydrogen atoms into each kink as a splint would support a broken bone.

The straightened-out FA molecules can now pack together more compactly, like a bundle of twigs that have had all their crooked twiglets trimmed off. Fats containing these compacted FAs therefore become harder and less fluid. If your soybean- or sunflower-oil margarine hadn't been hydrogenated, you would be pouring it, rather than spreading it, on your toast. Manufacturers use hydrogenated oils in virtually every cake, cookie or cracker in your supermarket to make it smooth, rather than oily.

Partial hydrogenation straightens out only some of the kinks in the unsaturated FA molecules. The rest are left in their bent, unsaturated shapes. Complete hydrogenation straightens out all the kinks in the FA molecules, making the fats completely saturated, and that's not good.

TRANS FATTY ACID A trans FA is an unsaturated FA that has been subjected to hydrogenation, but was able to evade the hydrogen atoms and remain defiantly kinky and unsaturated. However -- and this is the crucial distinction -- in the fiery cauldron of hydrogenation, its kink has been twisted into an angle different from that of a normal unsaturated FA. Chemists call this shape of FA a "trans" fatty acid.

Trans FAs are rarely found in nature; they are unnatural. When we eat a trans FA, our metabolism is baffled by its alien kinkiness and doesn't know what to do with it. So it vents its frustration not only by raising our LDL ("bad") cholesterol level, as saturated FAs do, but also by lowering our HDL ("good") cholesterol level. That double whammy is just about the worst thing a fat can do to us.

Complete hydrogenation, by the way, as distinguished from partial hydrogenation, does not form trans FAs, because when all of the kinks in an unsaturated FA are straightened out -- no escapees -- there are no unsaturated kinks left, either natural or trans. Not that the resulting saturated fats aren't harmful, but at least they are not as harmful as trans FAs.

Trans fatty acids are commonly but erroneously referred to as "trans fats," but they are not the entire fat molecules. They are merely the fatty-acid parts. The Food and Drug Administration has declared that the only acceptable amount of trans FAs in our diets is zero. Manufacturers don't "add trans fats" to foods, as I have seen stated. What they do is use partially hydrogenated fats for their desirable properties, and trans FAs are an inevitable result. When you see "partially hydrogenated" on a food label, you can bet that trans FA villains are in there. But if the product contains less than half a gram of trans FAs per serving, the FDA permits the label to say "No trans fats."

On the labels of manufactured foods, the amounts of trans FAs have customarily been incorporated into the total amounts of unsaturated FAs. But beginning on Jan. 1, 2006, the FDA will require the amounts of trans FAs to be stated separately. Manufacturers are engaged in a frantic scramble to achieve the benefits of partial hydrogenation without generating the concomitant trans FAs.

As they begin to succeed, we will see more and more food labels flaunting the words "no trans fats," just as they have flaunted the words "low calorie," "low fat," "low sodium" and "low carb."

I wonder how long it will be before we see labels reading "contains nothing at all"?

Robert L. Wolke is professor emeritus of chemistry at the University of Pittsburgh. He can be reached at wolke@pitt.edu.

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