A Straight Dope Classic from Cecil's Storehouse of Human Knowledge

What's the truth on trans fat?

December 22, 2006

Dear Cecil:

What's the Straight Dope™ on trans fat? My friend the medical student says the latest studies show that even a minuscule amount of trans fat causes a huge increase in heart disease and sudden heart attacks. Meanwhile, the FDA allows foods that list partially hydrogenated oils among their ingredients to claim to have zero grams of trans fat, as long as they have less than half a gram. Is any trans fat safe? If not, why is the FDA allowing companies like Frito-Lay to weasel?

Judging from what I'm seeing in blogs and such, people just aren't getting this trans fat thing, despite the uproar surrounding New York's recent ban of manufactured trans fats in restaurants. It's not about Big Brother, you dopes. ("Will they ban sugar and salt next?" Sheesh.) We're talking about an industrial product used in food preparation because it's cheap and convenient, not because it makes anything taste better. In the old days, when nobody knew trans fats from transvestites, the stuff seemed harmless. Now several big studies strongly suggest trans fat is even worse than saturated fat, formerly the hemlock of American cuisine.

Let's take it from the top. Although some trans fat occurs in foods naturally (mostly in animal products), the major source in the U.S. diet is partially hydrogenated vegetable oil. Hydrogenation, in which hydrogen gas is forced into oil under pressure, reduces rancidity and makes the otherwise liquid oil semisolid at room temperature, both useful features in products like margarine. Trans fat is created as a side effect of this process. It's similar to the other two common types of fat, saturated and unsaturated, except the carbon and hydrogen atoms are put together differently - where unsaturated fat molecules have a pronounced kink in the middle, trans molecules are straighter, more like those of saturated fat.

Why should this matter healthwise? Damned if I know (nobody else seems to have much idea either), but it does. One long-term study of more than 80,000 women showed that, compared to carbohydrates, every 5 percent increase in saturated fat consumption resulted in a 17 percent increase in the risk of coronary heart disease, while every 2 percent increase in trans fat resulted in a 93 percent increase. Interestingly, the study found that consuming more non-trans unsaturated fat relative to carbs reduces the risk of heart disease.

While it's difficult to eliminate trans fats from your diet completely (even vegans have to keep an eye out), the experts recommend consuming as little as possible - the stuff has no known health benefit. Official guidance is none-too-helpfully expressed in terms of grams and percentages. Better you should follow a few simple rules:

(1) Read the labels. Used to be you had to scan the fine print looking for "partially hydrogenated" in the ingredients list. Not any more - food companies are now required to quantify the saturated and trans fat in the nutrition labels on their products. You want trans fat to be zero and saturated as close to that as you can get.

(2) Hard fat is bad, soft or liquid fat is . . . well, not necessarily good (tropical oils such as coconut and palm are high in saturated fat), but more likely to be OK. Remember, saturated animal fat and partially hydrogenated vegetable oil are solid or viscous at room temp. I won't get into the Mac-versus-PC-like margarine-butter debate, but soft or liquid margarine is better than the stick kind.

(3) Avoid junk food. Familiar advice, sure, but look at this list of high-trans-fat edibles: crackers, cookies, doughnuts, and other snack foods (commercially produced baked goods in general are suspect), fried foods including fried chicken and French fries - are we seeing a theme here? The fast-food industry is edging toward eliminating trans fats (see below), but isn't there yet. If you like tiptoeing through a minefield trying to figure out what fast-food items from what chain are safe, have at it. Otherwise, drive on, Jack.

Why does the FDA allow foods with small levels of trans fat to claim zero content? Ostensibly because it's hard to accurately measure trans fats below 0.5 grams per serving, although I notice the cutoff under Canadian labeling rules is 0.2 grams. Even at the current limit, the FDA estimates trans fat labeling will prevent 2,500 to 5,600 deaths per year due to coronary heart disease.

The food industry is under pressure to dump trans fats. Wendy's has switched to a healthier cooking oil, KFC and Taco Bell have announced a similar change, and Disney hopes to remove added trans fats from its theme parks by the end of 2007. New York has taken the regulatory plunge, and Chicago is mulling it over. You can argue whether governments have any business legislating against the citizenry's slow suicide. All I'm saying is, trans fats are thought to be a factor in at least 30,000 deaths a year. Why let one of them be yours?

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