How to Spot Sneaky Fat: The Truth About Hidden Trans Fats
What Is Trans Fat?
To understand what a trans fat is, you first need a short primer on fats. Fats come in solid or liquid form and are a combination of saturated fat -- which is bad for your heart -- and unsaturated fat, which is not. Some fats are higher in saturated fat and others have more of the unsaturated variety.
Saturated fat, which raises cholesterol, is found in animal products -- think butter, whole milk, and steak -- and in tropical oils such as palm and coconut. Unsaturated fats, which can lower LDL (bad) cholesterol, are always liquid and found in vegetable oils. They come in two forms: monounsaturated (olive and canola oils) and polyunsaturated (safflower, sunflower, corn, and soybean oils). All fats are calorie dense, so eat even good ones in moderation.
Unlike the natural trans fats found in milk and some meats, man-made trans fatty acids are by-products of heating polyunsaturated liquid vegetable oil in the presence of hydrogen, which is done to create a fat that remains solid at room temperature and that won't go bad as quickly -- useful traits for cooking. The resulting partially hydrogenated fat is the artery clogger. (In a similar process, polyunsaturated oil can be fully hydrogenated, which makes it even more solid. This form doesn't have quite as harmful an effect on cholesterol levels, but is less useful for cooking.)
Trans fats were developed because they're cheaper to produce in mass quantities than animal fats, such as butter, and they can be reheated over and over again without breaking down. In the '60s, when heart-disease concerns were raised about saturated fats, some research claimed that margarine -- which is made from trans fats -- was healthier than butter, and food makers began to use trans fats widely. But since the '90s, evidence has been accumulating that trans fats may be even worse for the heart than butter.
We all know the dangers of saturated fat. It raises your LDL cholesterol, causing a buildup of plaque in your arteries, which in turn can cause heart disease. But at least saturated fat leaves your HDL alone, or slightly raises it (though you shouldn't turn to it to bump up your good cholesterol).
Trans fats, however, deliver a damaging one-two punch: They not only raise your LDL, they also lower your HDL. In one study, researchers found that replacing a diet high in heart-healthy monounsaturated fats (such as olive or canola oil) with a diet high in trans fatty acids increased LDL cholesterol by 14 milligrams per deciliter of blood and decreased HDL by 7 mg per deciliter. While replacing monounsaturated fat with saturated fat (such as butter) caused a similar rise in LDL, it had no effect on HDL. Trans fats also boost blood levels of C-reactive protein (CRP), a marker for inflammation that has been associated with heart disease, according to a study published in the Journal of Nutrition.
In fact, trans fats are so bad for the heart, says Dr. Stampfer, that if you replaced just 2 percent of the calories in your diet that now come from carbohydrates with trans fat, your risk for heart disease would skyrocket by 93 percent.