Trans Fats Exposed
Harvard School of Public Health - Fats and Cholesterol - The Good, the Bad, and the Healthy Diet
Trans fatty acids are fats produced by heating liquid vegetable oils in the presence of hydrogen. This process is known as hydrogenation. The more hydrogenated an oil is, the harder it will be at room temperature. For example, a spreadable tub margarine is less hydrogenated and so has fewer trans fats than a stick margarine.
Most of the trans fats in the American diet are found in commercially prepared baked goods, margarines, snack foods, and processed foods. Commercially prepared fried foods, like French fries and onion rings, also contain a good deal of trans fat.
Trans fats are even worse for cholesterol levels than saturated fats because they raise bad LDL and lower good HDL. They also fire inflammation,(6) an overactivity of the immune system that has been implicated in heart disease, stroke, diabetes, and other chronic conditions. While you should limit your intake of saturated fats, it is important to eliminate trans fats from partially hydrogenated oils from your diet. (Manufacturers must now list trans fats on the food label, right beneath saturated fats.)
Trans fats are a type of mostly man-made fat that the food industry loves, but our hearts and blood vessels don't.
Today we know that eating trans fats increases levels of low-density lipoprotein (LDL, "bad" cholesterol), especially the small, dense LDL particles that are most damaging to arteries. It lowers levels of high-density lipoprotein (HDL) particles, which scour blood vessels for bad cholesterol and truck it to the liver for disposal. It increases the tendency of blood platelets to clump and form potentially artery-blocking clots. It also fires inflammation, an overactivity of the immune system that has been implicated in heart disease, stroke, diabetes, and other chronic conditions.
This four-pronged attack on blood vessels translates into heart disease and death. Researchers estimate that eliminating trans fats from the U.S. food supply could prevent between 6 and 19 percent of heart attacks and related deaths each year--a staggering number, given that there are 1.2 million heart attacks and related deaths in the U.S. annually.
Recent studies on the potential cholesterol-raising effects of TFA have raised public concern about the use of margarine and whether other options, including butter, might be a better choice. Some stick margarines contribute more TFA than unhydrogenated oils or other fats.
Because butter is rich in both saturated fat and cholesterol, it's potentially a highly atherogenic food (a food that causes the arteries to be blocked). Most margarine is made from vegetable fat and provides no dietary cholesterol. The more liquid the margarine, i.e., tub or liquid forms, the less hydrogenated it is and the less TFA it contains.
Saturated fat is the main dietary cause of high blood cholesterol. Saturated fat is found mostly in foods from animals and some plants. Foods from animals include beef, veal, lamb, pork, lard, poultry, butter, cream, milk, cheeses and other dairy products made from whole and 2 percent milk. All of these foods also contain dietary cholesterol. Foods from plants that contain saturated fat include coconut, coconut oil, palm oil and palm kernel oil (often called tropical oils), and cocoa butter.