"Saturated fat is typically thought of as the "bad" fat since it has been linked to increased blood cholesterol levels. However, the evidence linking trans fatty acids to an increased risk of both heart disease and cancer is much stronger," says Mary Flynn, PhD, RD, a research dietitian at The Miriam Hospital specializing in the benefits of healthy food sources of fat. Flynn's research is based upon studies starting in the 1950s finding the lowest rates of cancer and heart disease were on the Greek Islands where the food is swimming in olive oil.
Trans fats are a specific type of fat that is formed when hydrogen is added to liquid vegetable oils to make them solid, like shortening and hard margarine. They act like saturated fats in that they raise levels of unhealthy LDL, or "bad" cholesterol, but they also lower levels of HDL, or "good" cholesterol.
"High LDL and low HDL levels are known indicators for an increased risk of heart disease, but trans fatty acids seem to compound the adverse effects on heart health even greater than what is usually expected from changes in LDL and HDL," Flynn notes.
Additionally, studies have shown that postmenopausal women with high levels of trans fatty acids can have as much as a 40 percent increase in their risk of breast cancer, and that consuming just five grams of trans fats a day-a typical serving of french fries - can increase a person's risk of heart disease by 25 percent.
"Ironically, food manufacturers started using trans fats as a healthier alternative to replace cooking with tropical oils, when in actuality it was more harmful than what they were originally using," says Flynn.
Restaurants, especially fast food eateries, adopted trans fats quickly because of their ability to extend the shelf life of the food they are used in, and add to the texture and flavor of fried and processed foods and baked goods.
"Although everyone agrees that trans fats are a major source of coronary artery disease, the challenge to the industry is finding a healthier substitute that will not alter the taste of some foods," says Flynn.
Flynn advocates cooking with olive oil as much as possible. Olive oil is monounsaturated oil that can actually help lower "bad" cholesterol and contains antioxidants that discourage artery clogging and chronic diseases, including cancer.
"Fat is an essential source of energy for our bodies; however, it's important to be able to distinguish the unhealthy sources from the healthy ones," she notes.