FOOD 101

Trans Fat Translation

Wednesday, August 20, 2003; Page F01

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I'm very confused about trans fats. I recently read that hydrogenated, partially hydrogenated and fractionated oils are considered trans fats. I then bought some tub margarine, which advertised that it contained no trans fats. However, on closer inspection of the label, I noticed that it contained fractionated oil. So, here are my questions: Are fractionated oils considered to be trans fats? What is the difference between fractionated and hydrogenated oil? And what does the "partially" add to the mix?

In light of recent developments, there has been a strong resurgence of interest and confusion surrounding trans fatty acids, or "trans fats." And may I say that your degree of confusion, if you will accept the compliment, is one of the most thorough that I have seen.

On July 11, the Food and Drug Administration issued its final rule on the labeling of foods containing trans fatty acids, to wit: "In this final rule and given the current state of scientific knowledge, FDA is requiring the mandatory declaration in the nutrition label of the amount of trans fatty acids present in foods, including dietary supplements." (Note that this new labeling is both "required" and "mandatory." I wouldn't be surprised if it were also compulsory and obligatory.) The rule is to become effective Jan.1, 2006.

As a consequence, people everywhere are asking, "What the heck is a trans fatty acid, anyway?" That's why I'm here.

It's not my bag to go into the detailed health consequences of ingesting trans fatty acids. For our present purposes, suffice it to say that trans fatty acids are b-a-a-a-d. They raise your total blood cholesterol level and your LDL, or bad cholesterol; lower your HDL, or good cholesterol; and are suspected of contributing to obesity and diabetes.

Whence fatty acids?

Trans fatty acids don't occur naturally, except for small amounts in a few plants such as pomegranates, cabbage and peas and in the meat and milk of cows, sheep and goats. They are created in much larger amounts during the hydrogenation of vegetable oils to make them more solid, most often to convert liquid soybean oil into a manageably spreadable margarine. In fact, trans fatty acids are in every food that says "partially hydrogenated vegetable [or a specific vegetable] oil" in the list of ingredients. You can assume that most everything on the snack food shelves of your local convenience store is loaded with trans fatty acids.

Understanding trans fatty acids requires digesting a bit of a chemistry lesson, and whether or not you hated chemistry in school, I'm going to lay it on you right here and now. So either hold tightly onto your coffee cup or skip below to the heading "Hide and seek."

Kinky molecules

A molecule of any fat (Techspeak: a triglyceride) contains three fatty acids. The three fatty acids can consist of any combination of saturated, monounsaturated or polyunsaturated. The health consequences of any given fat are purely those of the fatty acids it contains.

The fatty acids parts (let me call them FAs from here on) consist almost entirely of long chains of carbon atoms with attached hydrogen atoms. In a saturated FA, every carbon atom in the chain carries two hydrogen atoms. But in an unsaturated FA, there are occasional places where two adjacent carbon atoms have only one hydrogen atom apiece. In a sense, twice as much of the available bonding strength has been used between the carbon atoms, with none left over for grabbing two more hydrogen atoms. That's called a double bond. If there is one such location in a FA molecule, it is said to be monounsaturated; two or more make it a polyunsaturated FA.

Wherever a double bond occurs in an unsaturated FA, it makes a kink or bend in the otherwise straight chain. The bumpiness of these FA molecules prevents them from packing tightly together, so they tend to be runny liquids, rather than firm, well-packed solids. But even more significant is the fact that in all biological processes, the exact shapes of molecules can be enormously important. It's the shapes that make straight-chain saturated FAs less healthful than kinky unsaturated FAs.

Food manufacturers want to convert unsaturated liquid fats into more-saturated, semi-solid fats to make their products more consumer-friendly. So they employ high temperatures and pressures to force two more hydrogen atoms into the double bonds. That is, they hydrogenate the unsaturated FAs to make them more saturated.

But if they were to saturate every single double bond in a polyunsaturated FA, it would become so solid and hard that it would be as inedible as candle wax. That's why liquid vegetable oils are only partially hydrogenated; only a fraction of their double bonds are filled in with hydrogen atoms.

Now here's the problem. During the hydrogenation process, the added pair of hydrogen atoms can settle into the double bond in either of two ways: both on the same side of the chain (Techspeak: in a cis conformation) or one on each side (Techspeak: a trans conformation). Cis, pronounced sis, and trans are from the Latin, meaning "on this side" and "across," respectively.

The two different resultant molecules (Techspeak: geometric isomers), even though having identical numbers of hydrogen atoms, behave differently because their shapes are different. The cis molecule has a kink in its chain where the hydrogen atoms were added, making it resemble an unsaturated FA, whereas the trans molecule is relatively straight, resembling a saturated FA. We all know that saturated FAs are cholesterol-producing villains, and so then are the similarly shaped trans FAs.

Hide and seek

Until the FDA's required, mandatory, compulsory and obligatory labeling takes effect, how can you tell where all the trans FAs are hiding? You're not going to like this, but partially hydrogenated fats, carrying their burden of trans FAs, lurk in virtually everything you love to eat: margarine, commercial cakes and cookies, doughnuts, potato chips, crackers, popcorn, nondairy creamers, whipped toppings, gravy mixes, cake mixes, frozen French fries and pizzas, fish sticks and virtually all fried foods, unless you fry them yourself in un-hydrogenated oils. But trans FAs are also formed by the high temperatures of frying, so you may be making them yourself. And to make things worse, restaurants that brag about using only "pure vegetable oil" don't tell you that it's probably been hydrogenated.

There is, however, a ray of hope. The amounts of trans FAs formed in the hydrogenation of oils depends on the temperature, hydrogen pressure, length of exposure and many other factors. Now that the pressure is on from the Feds, you can bet your Twinkie that packaged food manufacturers will accelerate their efforts to find ways of attaining the desired physical characteristics in their fats with minimum production of trans FAs. They want to earn the right to put the coveted phrase, "Contains no trans fatty acids," or "Contains no trans fats," on their labels.

Oh, and about fractionated oils: Fractionation does not add or remove trans fatty acids from an oil. All it does is remove some of the more saturated fats -- trans or not -- to keep the product from thickening when stored in a cool place.

Department of occupational hazards: The catalogue of Chef Revival USA, Inc., a supplier of culinary apparel and equipment "designed by chefs for chefs," includes chefs' pants and jackets in waist sizes up to 71 inches and chest sizes up to 80 inches.

Robert L. Wolke (www.professorscience.com) is professor emeritus of chemistry at the University of Pittsburgh and the author, most recently, of "What Einstein Told His Cook: Kitchen Science Explained" (W. W. Norton, hard cover, $25.95). He can be reached at wolke~pitt.edu.

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