Why? Because trans fat is being replaced by new and sometimes unfamiliar ingredients.

Trans fats are created when vegetable oil is partially hydrogenated, a process that converts liquid oils into solid or semisolid forms used in shortening and some margarines. Research shows that trans fats -- as well as saturated fats -- raise levels of LDL, or "bad" cholesterol, and lower levels of HDL, or "good" cholesterol, increasing your risk of coronary artery disease.

The federal government now requires food manufacturers to list on the nutrient facts label the amount of trans fat in packaged foods. Since trans fat is no longer hidden from shoppers, food companies are testing alternatives.

Palm oil is one of them.

One reader wrote to me: "Recently I discovered that Food Lion's 'Honey Flavored Graham Crackers' labeled 'cholesterol-free' have no hydrogenated oil. But they have palm oil, which my wife believes is still bad for me."

His wife is probably right.

Palm oil is made from the pulp of palm tree fruit and is used all over the world in margarine, cookies, crackers and baked goods -- the same foods in which trans fat-laden partially hydrogenated oils have been used in the U.S.

Palm oil is cheaper than other vegetable oils, but it's probably not as good for your health. Though it's likely not as damaging as the saturated fat in butter or the trans fat in partially hydrogenated vegetable oil, palm oil does increase blood cholesterol levels.

More research is needed to better understand how different forms of fat affect health, but for now, most health scientists think eating palm oil raises the risk of coronary artery disease and that we should limit the amount we eat.

What else is being used to replace partially hydrogenated oils?

• Interesterified oils. These are vegetable oils that, like partially hydrogenated oils, have been chemically altered so that they are solid or semisolid at room temperature.

A study published last year at Brandeis University found that interesterified oil had a similar, though slightly lesser, effect on blood cholesterol levels as compared to trans fat. However, interesterified oil also appeared to raise blood sugar levels. Until there's been more study of this type of oil, avoid it.

• Mixed vegetable oils. Some manufacturers are using a blend of several different oils, including corn, soybean, canola and others. Assuming these ingredients aren't preceded by the words "interesterified" or "partially hydrogenated," they're fine.
• Butter, lard and other animal fats. These contain saturated fat, which, like trans fat, is linked with higher cholesterol levels and an increased risk for coronary artery disease. Eat as little as you can.

Also keep these tips in mind:

• Do it yourself. If you want cookies or cake, bake your own using liquid vegetable oil or trans fat-free margarines you can find at natural foods stores.
• Tally the combined trans fat and saturated fat. When you read a food label, add the number of grams of trans fat and saturated fat the food contains per serving. Keep the grand total to less than 15 grams per day for most people. Better yet, hold it to the single digits if you can.
• Buy more at natural foods stores. It's not a guarantee that what you buy will be good for you (yes, there is such a thing as natural junk food). But most natural foods stores shun products that contain partially hydrogenated oils and other chemically altered or artificial ingredients.

The movement away from trans fat in foods is a public health victory. As replacements are found, though, it'll be as important as ever to pay attention to food labels.