Trans Fats Are Bad, Aren’t They?

The media have been rife with reports on trans fats since New York City’s Board of Health announced it would phase out these fats in restaurants and other food-service establishments. And that’s good news for most consumers because trans fats can pose a double whammy for the heart. Not only can they hike a person’s bad cholesterol even more than saturated fats can, but they also reduce concentrations of the good cholesterol in blood.

CHEESY EXCEPTION. The trans fats known as conjugated linoleic acids (CLAs), which form naturally in animals, show up in meats and dairy products, such as this cheese. It’s not the type of fat that the New York City ban is targeting. Photodisc

Not surprisingly, these largely synthetic fats—designed to stay solid at room temperature, as saturated fats do, and typically used in fried foods and bakery items—have been linked to ailments ranging from coronary heart disease to diabetes (SN: 11/10/01, p. 300).

So, good riddance. Right?

Well, as with so much in science, there are caveats. And there’s a big one with the trans fats. Although the vast majority of these fats are unhealthy, there is a minority that are fine to eat and may even prove beneficial.

Known as conjugated linoleic acids (CLAs), some of these trans fats occur naturally in dairy products and meat, especially milk and butter. Others form as a result of chemical processing or cooking. A growing number of studies have demonstrated that, at least in animals, these unusual fats fight a host of chronic health conditions from heart disease to diabetes to cancer (SN: 3/3/01, p. 136). Most recently, several CLAs have shown promise in moderating the runaway inflammation that underlies arthritis, asthma, and even lupus (see Inflammation-Fighting Fat).

A new line of research now aims at naturally increasing the concentrations of these unusual trans fats in foods such as milk and cheeses. Michael W. Pariza of the University of Wisconsin–Madison, who discovered the beneficial alter ego of CLA trans fats more than 2 decades ago, suspects that one day they may even be added to foods to fortify their healthiness.

At present, however, most people take in minimal amounts of CLAs.

Nevertheless, data on the potential benefits of these unusual trans fats have been so compelling that the Food and Drug Administration exempted them from the new trans-fat labeling law that went into effect this year (see No Hiding Most Trans Fats). That law had been intended to steer people away from bad fats.

Meanwhile, research continues to malign the synthetic trans fats being targeted by New York City and other health departments. For instance, a major review of the health implications of current U.S. consumption patterns of trans fats appeared in the April 13 New England Journal of Medicine. Walter C. Willett of the Harvard School of Public Health, in Boston, and his colleagues reported that some 2 to 3 percent of people’s daily calories typically come from the synthetic trans fats.

Willett’s team found that largely eliminating bad trans fats in U.S. diets could improve people’s blood cholesterol enough to cut heart attacks and other cardiovascular problems by 3 to 6 percent. That would be up to 72,000 fewer such adverse events per year, the team said. Even better, other advantages from such a dietary shift, such as improved immune systems, could eliminate another 150,000 or so adverse heart events per year.

The team’s report also briefly addresses CLAs and notes that they aren’t the kind of trans fats that researchers are worried about.

There is one more important caveat about CLAs: As fats, they’re high in calories. That means that, as with all energy-dense foods, consumption of their food sources should be kept within moderation.

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Janet Raloff

Janet Raloff is the Editor, Digital of Science News Explores, a daily online magazine for middle school students. She started at Science News in 1977 as the environment and policy writer, specializing in toxicology. To her never-ending surprise, her daughter became a toxicologist.

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