I first remember hearing about trans fats in the mid 1990s when reports that margarine, which had been touted by the manufacturers as healthy, contained them and may not be so healthy after all. It turned out that trans fats were in most processed foods in the supermarket and in many fast foods. In 1994 Harvard researchers went so far as to conclude that trans fats were indeed responsible for more than 30,000 deaths yearly from heart disease in the United States alone.
When manufacturers add hydrogen to corn, soybean and other highly unsaturated oils to make them more solid and stable the polyunsaturated and monounsaturated fatty acids, which are good fatty acids become saturated. This is called hydrogenation or partial hydrogenation in some cases. This also transforms the chemical structure of some unsaturated fatty acids in other subtle ways, producing trans fatty acids or trans fats. Hydrogenation gives margarines, shortening, and puddings a creamy consistency, and prolongs the shelf life of crackers, cakes, cookies, chips, popcorn, chocolate, and other foods. Because they are less likely to turn rancid hydrogenated oils are often used for deep-frying in fast food restaurants.
While regular unsaturated fats lower blood cholesterol, trans fats act more like saturated fats-raising total and LDL ("bad") cholesterol. In addition , in a sort of double whammy, trans fats lower HDL ("good") cholesterol, which makes them, overall, even worse than saturated fats. They also increase the risk of heart attacks in other ways: for instance, they boost blood triglyceride levels and seem to impair the ability of blood vessels to dilate. They have also been linked to an increased risk of diabetes.
A 1993 study of more than 90,000 women found that those who ate the most foods high in trans fats (especially margarine) had a more than 50% higher risk of heart disease than women who rarely ate them. Two Dutch studies also found increased coronary risk among people who consume high levels of trans fats.