Trans fats are the latest health threat to worry about. They put on weight and can clog your arteries by boosting so-called “bad” cholesterol and lowering the “good” cholesterol that helps keep the arteries clear.

But they taste so good. Consumer Reports called trans fat “the stealth fat,” and cited a ready-to-eat apple pie as a cautionary example. The label says a slice contains 3.5 grams of saturated fat (a well-known artery clogger). Consumer Reports found also 4 grams of trans fat – “invisible,” because it didn’t have to be labeled. The combination gave that slice of pie a worse rating than any other product in its table “Bad Fats in Common Foods.”

At long last the U.S. Food and Drug Administration is doing something about it. The agency issued a rule requiring food manufacturers to list the amount of trans fats in their product labels starting Jan. 1, 2006. But some companies are already reducing the trans-fat content in their products, among them Kraft Foods and McDonald’s. The Wall Street Journal reports that Frito-Lay has reduced or removed trans fats from its Doritos, Tostitos and Cheetos snacks and added the trans-fats line to its labels, and that Legal Seafoods has started using reduced trans-fat oil to fry its fish and switched to an oyster-cracker supplier that doesn’t use trans fats.

But some companies find it tough to change without hurting taste or texture. Kraft isn’t sure when it can cut trans fats from its Oreo cookies (2.5 grams per thee-cookie serving).

In the meantime, says Consumer Reports, nutrition specialists urge that people limit their intake of both bad fats, for the sake of their hearts and their weight. Some say the total should be less than 10 percent of total daily calories, or about 22 grams on a standard 2,000-calorie diet. Watch out for products heavy on partially hydrogenated oils or saturated fats. Take soft or liquid margarine instead of hard types. And when buying oil, choose olive oil or canola oil, which contain good cholesterol.

The FDA action relied on a six-month study that found that the number of overweight children had nearly doubled and the number of overweight adolescents had nearly tripled in the past 20 years. It said that about 300,000 deaths a year in this country are associated with being overweight or obese, at an estimated cost of $117 billion in 2000. That doesn’t count the cost of the apple pie.