Americans are aware of what too much cholesterol can do to people. High-fat diets cause many patients' problems. More and more Americans are looking at food labels to know what they consume.

Now, new rules on food labeling will make it easier for consumers to avoid trans fats, which plug arteries, and have been linked to an increased risk of heart disease, among other things.

Trans fats are a result of manufacturers adding hydrogen to vegetable oils to improve shelf life. If a product is labeled "partially hydrogenated," it means at least some trans fats are created in the product, the amount ranging from almost zero to a large portion of a food item's calories.

The partially hydrogenated vegetable oils that contain trans-fatty acids make baked goods and fried foods crispy or crunchy. They make doughnuts creamy. They extend shelf life, are solid at room temperature, and are cheaper than other types of fat. They affect how a product tastes, sometimes in hard-to-duplicate ways.

Trans fats can wreak havoc on humans, lowering good cholesterol, raising bad cholesterol and reducing the quality of everything from testosterone to breast milk.

They are worse than saturated fats that nutritionists have long warned about. Saturated fats raise the level of bad cholesterol, but they also provide some health benefit by raising the level of good cholesterol.

The labels have already had an impact. Rather than face an undesirable label, many large food manufacturers have announced they will reduce or eliminate trans fats.

Though trans fats are found in small quantities naturally in dairy products, most Americans get their trans fats through heavily processed foods such as vegetable shortening, margarine, and snack foods like deep-fried chips and packaged breads, cookies and crackers.

Dieticians recommend that it is best to keep trans fat consumption as close to zero as possible.

In response to rising health concerns, the U.S. Food and Drug Administration (FDA) set the new labeling requirements in 2003. Many food labels already contain trans fat listings. companies have rolled out their new labels as their supplies of old ones ran out.

But not every new label will be in place on Sunday, as stores use up products with old labels. The idea behind the labeling is to give consumers more information they can use to make healthier choices. To find trans fats, when they're listed, look under the "Saturated Fat" listing, just under the "Total Fat" heading.

Also, some trans fat content can still receive a zero trans fat listing under the new rules, even if a hydrogenated oil is an ingredient. If a food has less than 0.5 grams of fat per serving and makes no claims about fat content, manufacturers can skip the label. If a product simply has less than 0.5 grams of trans fat, the FDA allows a company to list its trans fat content as zero.

Trans fat awareness has also made companies to remove it from their own foods, fearing that consumers may not eat trans fatty products once they know their content. Frito-Lay and Kraft, among food companies, have dramatically reduced the number of products they sell that contain trans fats.

Food activists are calling for labeling in restaurants. Restaurants have also jumped on the no-trans wagon. Panera Bread is switching from partially hydrogenated oil in its baked goods to butter and palm oil.

Food advocate groups are pushing for more regulation. The Center for Science in the Public Interest, a Washington-based watchdog group that has roots in Ralph Nader-led advocacy, is calling for labeling of trans fat on restaurant menus - doughnuts, french fries and other popular restaurant items are also high in trans fats, and right now aren't regulated.

Many groups are pushing for directions to restaurants that choose trans fat-laden cooking oils over healthier alternatives to add health information to their menus so consumers can make better choices in restaurants, too. It would cost companies $ 854 million over 20 years to change labeling and reformulate food in ways that preserve quality while cutting trans fat. Much of the cost will be absorbed by companies.

And the public health benefits could be great - the FDA projects savings of between $25 billion and $59 billion in health care costs over 20 years.