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.
