Trans Fats: The Science and the Risks
This man-made fat was developed to protect us against butter. Turns out, it acts like butter inside our bodies.
By Denise Mann
Reviewed By Louise Chang, MD
What exactly are trans fats? How are they made? How bad are they, really? And just how solid is the science that the FDA consulted when they voted to list trans fats on nutrition labels? To get to the bottom of these and other questions about trans fats, WebMD spoke to leading nutritionists.
Why hydrogenate? Hydrogenation increases the shelf life and flavor stability of foods. Indeed, trans fats can be found in a laundry list of foods including vegetable shortening, margarine, crackers (even healthy sounding ones like Nabisco Wheat Thins), cereals, candies, baked goods, cookies, granola bars, chips, snack foods, salad dressings, fats, fried foods, and many other processed foods.
Trans fatty acids are found naturally in small quantities in some foods including beef, pork, lamb, butter, and milk, but most trans fatty acids in the diet come from hydrogenated foods. So there is good news: When the new nutrition labels go into effect Jan. 1, 2006, it will be easier to screen these fats out of your diet. Until then, look at the package's list of ingredients. Products that contain partially hydrogenated oils or vegetable shortening may contain trans fats.
Where Did Trans Fats Come From?
Trans fats were developed during the backlash against saturated fat -- the artery-clogging animal fats found in butter, cream, and meats. Then food manufacturers realized that trans fats lasted longer than butter without going rancid. The result: Today trans fats are found in 40% of the products on your supermarket shelves.
"We used to use animal fats, and people said, 'saturated fats are bad,' so we switched to trans fats," says Ruth Kava, PhD, RD, director of nutrition at the New York City-based American Council on Science and Health. "This kind of gives us an unfortunate focus on ingredients rather than the whole diet when the problem isn't this fat or that fat, it's too many calories."
"Anything was good if it decreased saturated fat consumption in the 1950s through the 1980s," agrees Alice H. Lichtenstein, Dsc, professor of nutrition at Tufts University in Boston. "But then studies began to question trans fats," too. Finally, in the 1990s, the evidence became clear: When vegetable oil is turned into a solid, like butter, it acts like butter inside the body.
Next, learn about the risks.
What Do Trans Fats Do Inside the Body?
Like saturated or animal fats, trans fats contribute to clogged arteries. Clogged arteries are a sign of heart disease; they increase your risk of both heart attack and stroke. Here's how it works: Trans fats raise low-density lipoprotein (LDL) or "bad" cholesterol levels. This contributes to the buildup of fatty plaque in arteries.
"The science that shows that trans fats increase LDL cholesterol levels is outstanding and very strong. All evidence is pointing in the same direction," Lichtenstein tells WebMD.
In the Nurse's Health Study, women who consumed the greatest amount of trans fats in their diet had a 50% higher risk of heart attack compared to women who consumed the least.
Some researchers suspect that trans fats also increase blood levels of two other artery-clogging compounds -- a fat-protein particle called lipoprotein(a) and blood fats called triglycerides.
Equally worrisome, population studies indicate that trans fats may raise the risk of diabetes. Researchers at the Harvard School of Public Health in Boston suggest that replacing trans fats in the diet with polyunsaturated fats (such as vegetable oils, salmon, etc.) can reduce diabetes risk by as much as 40%.
How much trans fat is safe? No one really knows. Kava says the prestigious Institute of Medicine reported that there isn't enough research yet to recommend a safe amount of trans fats. "We know that like saturated fats, trans fats can raise bad cholesterol, but there is conflicting data about what it does to good cholesterol," she says. "I wish the data were stronger."