NEW ORLEANS, Nov. 12 – A new study sheds light on whether a dietary fat called trans fat, found in many baked goods and fried foods, increases a person’s risk of heart disease, according to researchers who presented their results at the American Heart Association’s Scientific Sessions 2000.
“While the dangers of the saturated fat found in high-fat meat and dairy products are well known, the situation on trans fatty acids is not so clear,” says lead author Alice H. Lichtenstein, D.Sc., a professor of human nutrition at Tufts University, Boston.
Trans fatty acids are created by the hydrogenation of vegetable oils. Food manufacturers use hydrogenation to make polyunsaturated liquid vegetable oil solid at room temperature. The process lengthens the shelf life of packaged baked goods like cookies, crackers, pastries and donuts.
Commercially fried foods also contain significant amounts of trans fats. The topic is under scrutiny because the Food and Drug Administration is considering adding information on trans fatty acids to food labels, explains Lichtenstein, a researcher at the Jean Mayer USDA Human Nutrition Research Center on Aging at Tufts.
“We’re trying to give people the best advice possible on how to modify their diets to reduce heart and blood vessel disease risk,” she says. “There are many unresolved issues.”
One of the unresolved issues is how to weigh the relative importance of dietary restrictions on saturated fats and trans fatty acids. While the two substances have similar effects in the body, they are not the same, Lichtenstein says. Saturated fats make up 12 to 13 percent of the U.S. diet (the American Heart Association dietary guidelines recommend a 10 percent limit) versus about 2 percent of total calories for trans fatty acids.
“The issue is further clouded because there is incomplete information regarding trans fatty acids and consumers are unable to gauge their intake because trans fatty acids are not listed on food labels,” she says.
Everyone’s cholesterol, or blood fat, profile contains a variety of components such as low-density lipoprotein cholesterol (LDL) and triglycerides – both of which are thought to increase the risk of heart disease – and high-density lipoprotein cholesterol (HDL), which is believed to help clear cholesterol from the body.
In this study, 26 volunteers were fed in rotating, five-week dietary phases in which their fat sources were randomly assigned. All diets had 30 percent of calories from fat with 20 percent of the fat coming from either soybean oil, semi-liquid margarine, tub margarine, shortening, stick margarine or butter. “We were interested in assessing what would happen when we substituted one fat for another,” Lichtenstein says.
The researchers found as the trans fatty acids increased and polyunsaturated fats decreased due to greater hydrogenation, the triglyceride levels four hours after a meal increased. In fact, the stick margarine diet caused triglyceride levels to rise 18 percent higher on average than did the diet that used semi-liquid squeeze bottle margarine. Stick margarine also caused a drop in HDL, the “good” cholesterol. Although butter increased HDL levels, it also caused a significant increase in LDL, considered one of the most dangerous components of total cholesterol.
“The best dietary advice we can give people is to minimize their intake of animal and hydrogenated fats in order to reach the American Heart Association’s target of 10 percent or less of total calories from saturated fat and trans fatty acids,” she says. “That would mean consumers choosing low fat and non-fat dairy products and lean cuts of meat, and the food industry decreasing the amount of hydrogenated fats used in their products.”
Co-authors include Lynne M. Ausman, D.Sc.; Susan M. Jalbert, B.S.; Ernst I. Schaefer, M.D.
NR00-1180 (SS2000/Lichtenstein)