When major food companies began widely using partially hydrogenated oils in the 1970s, they thought they were making their products more healthful. Consumer groups and regulators applauded the industry's switch from heavily saturated fats, such as lard and palm oil.

But the evidence is growing that the trans fatty acids in partially hydrogenated oils are damaging to the heart too -- and more so than other kinds of fats. Once again, the food industry is looking for an alternative fat, only this time there doesn't seem to be an easy answer.

"It isn't simple, it isn't cheap, and it isn't going to happen overnight," said Robert M. Reeves, president of the Institute of Shortening and Edible Oils, a Washington trade group.

The impetus for the change is a Food and Drug Administration ruling last year that by January 2006 all packaged food products have to list on their nutrition labels the amount of trans fatty acids, or trans fat, they contain. That ruling puts pressure on manufacturers to replace oils containing trans fatty acids before the deadline, company officials say, because no one wants to advertise another ingredient implicated in heart disease, along with the already required disclosures on saturated fat and cholesterol.

Though a few major players, such as Frito-Lay Inc. and Pepperidge Farm Inc., have already made the switch to other oils, industry officials said many other companies won't be able to make the change in time. They say that's because alternative oils have their own health problems, are too expensive, or can't be substituted without changing the taste, texture or shelf life of a product.

"The amount of trans fat will be labeled on the product by January 2006. Whether all the products are reformulated, that's unlikely," said Alison J. Kretser, director of scientific and nutrition policy for the Grocery Manufacturers of America (GMA). "It's not for lack of trying."

Food companies are spending millions of dollars researching, evaluating and testing various fat alternatives, Kretser said, but experts in the food and oil industries say it still could be five to 10 years before trans fats can be effectively replaced.

"Trying to find that functionality and get it to the American consumer in a timely way is a very great challenge," Reeves said. "Some of the options that we have will take a while to develop."

The industry effort doesn't get a lot of sympathy from Michael F. Jacobson, executive director of the Center for Science in the Public Interest (CSPI), which first petitioned for the labeling of trans fats 10 years ago and has called for an outright ban on their use. Studies have shown trans fat prompts increases in levels of bad cholesterol and decreases in good cholesterol, Jacobson said, and "the short answer is that anything is better than trans fat."

Trans fatty acids are created when a liquid oil, such as vegetable or soybean oil, is put through a process called hydrogenation. That makes it more solid and gives it physical characteristics that are beneficial for commercial food operations, such as the ability to be spread, texture and a longer shelf life.

Manufacturers like it because the process can be stopped at any time to create a fat with any type of texture, depending on how many hydrogen atoms are forced onto the underlying fat molecule. The result could be a liquid oil that is altered just enough to give it a longer shelf life, a creamy fat that's perfect for cookies and pie crusts, or a fully hydrogenated fat that is hard at room temperature.

The trick is finding an alternative. And right now the perfect one doesn't seem to exist.

"Everything has its pros and cons," Reeves said.

One choice would be simply going back to using tropical oils, which are cheap. For foods that use only liquid fat in the manufacturing, tropical oils can readily replace partially hydrogenated oils, because they are naturally stable; they have a longer shelf life than regular soybean or corn oil, which go rancid more quickly.

But tropical oils have a big downside: They are heavily saturated, so their use would replace one bad kind of fat with another. And a major increase in demand by the U.S. food industry would vastly exceed even the ready supply that's available.

CSPI has still other concerns about ramping up production of these oils, which come largely from Indonesia and Malaysia.

"The growing of oil palms in Southeast Asia typically destroys wildlife habitats, killing elephants and tigers and orangutans," Jacobson said. "The processing plants pollute the environment. So there are problems from different dimensions."

Frito-Lay and Pepperidge Farm were able to switch relatively easily from partially hydrogenated oils to more healthful, non-hydrogenated oils, such as corn and sunflower oils, company officials said.

But other companies may not be able to use these oils. Even though they are actually beneficial to heart health, they do not work for many baking applications that need a creamier fat. They may impart a different taste and are more expensive.

"Our companies are beginning to do those things that they can -- things that are easier to switch," said Kretser of GMA.

Frito-Lay moved entirely to corn oil for its snack foods last year, but it is costing the company $30 million to $40 million a year extra in oil costs, said Rocco Papalia, senior vice president of research and development for the company. In its financial release for 2003, Frito-Lay said that without the oil switch, its operating profit would have grown by an additional 1 percent, or about $22 million.

The company chose corn oil because it has a positive health profile and is widely available, but it was a chore to make it work without changing the taste and texture of its products.

"It took us about 7,000 man-hours . . . and a few hundred sensory and taste tests to make sure the product was right," Papalia said. Production changes also had to be made on 200 manufacturing lines at 45 plants nationwide.

Frito-Lay's early adoption of corn oil also has made it more difficult for other companies that might want to do the same because its consumption of the oil pushed up the price.

Mark Ash, an agricultural economist with the Department of Agriculture's Economic Research Service, said the price of corn oil spiked last year to about 36 cents a pound -- or 20 percent more than the cost of soybean oil, which is the oil most commonly hydrogenated for food manufacturing.

Pepperidge Farm, meanwhile, started researching fat alternatives five years ago and will complete its transition to trans-fat-free sunflower oil, canola oil and un-hydrogenated soybean oil by the end of this year. The company had to change its dough mixing, sheeting and baking processes to create a Goldfish cracker that tasted the same, said Scott Gantwerker, vice president of research and development and quality assurance. The new oils are more expensive than hydrogenated soybean oil, he said, and harder to get in sufficient quantity. Ash said sunflower and canola oils typically cost 10 to 17 percent more than soybean oil.

"Hopefully supply and demand will take over and at some point the supply will increase and cost will go down," Gantwerker said.

Of course, what's a problem for some food processors is a business opportunity for others. Agricultural products giant Archer Daniels Midland Co. (ADM) has high hopes for its newly engineered oil. It mixes a fully hydrogenated, solid soybean oil -- which has a neutral effect on heart health -- with a liquid oil that has health benefits. In rearranging the enzymes on the fat molecules, ADM says, it is creating a product with a semi-solid texture that has good food-production properties but doesn't have the molecular structure that makes partially hydrogenated oils harmful.

ADM is meeting with commercial food manufacturers, said Mike Rath, general manager of specialty oils and fats. The company also is launching its own clinical trials to help establish the healthfulness of its new trans-fat-free oil.

But the product is not yet available in the quantities that food companies might need, and Rath said it is still more costly than most tropical and partially hydrogenated oils. Yet the price won't come down until ADM can ramp up production.

"We think over the long term . . . that we will have competitive prices," Rath said. "As you get more of the market to move in that direction, you get more efficient at it."

Another alternative still on the drawing board is genetically engineered soybean plants that would create oils with fatty acid profiles that are more favorable for health effects and cooking. Many experts have high hopes for such an alternative. But even if the right plant can be created, it would take years before enough fields were planted to produce the billions of pounds of oil the food industry requires.

And there's no guarantee that even this solution would solve the industry's problems in finding alternative fats, said Barry Swanson, a professor of food science and human nutrition at Washington State University.

"Just because they are genetically engineered soybeans, people may not be accepting of that," he said. "And as soon as the farmers switch crops, they've got different agricultural problems: different insects, different weeds, different climates. There are all kinds of problems they run into that nobody knows about."