So just what are trans fats? There are two types -- the naturally occurring type, found in small amounts in dairy and meat, and the artificial kind that results when liquid oils are hardened into "partially hydrogenated" fats. Natural trans fats are not the ones of concern, especially if you usually choose low-fat dairy and lean meats. The real worry in the American diet is the artificial trans fats, which are used extensively in fried foods, baked goods, cookies, icings, crackers, packaged snack foods, microwave popcorn, and some stick margarines.
These artificial trans fats started getting lots of attention after research showed that they could increase the risk for heart disease by increasing "bad" LDL cholesterol and decreasing "good" HDL cholesterol.
The American Heart Association (AHA) recommends limiting trans fat to less than 2 grams per day (a figure that includes the naturally occurring trans fats). The 2005 U.S. Dietary Guidelines simply recommend keeping trans-fats consumption as low as possible.