LOUISVILLE, Ky. — Just six weeks after the Louisville Metro Council banned smoking in the city's bars and restaurants, Councilman Dan Johnson is pushing to ban trans fats in the city's 2,600 eateries.

Johnson's proposal, which he plans to file this week, comes amid a national push to rid the nation's diet of trans fats.

While no large city has banned the substance in restaurants, New York City and Chicago are considering regulations, and several major fast-food and snack companies have voluntarily reduced the amount of trans fat they use or dropped it completely.

KFC, based in Louisville, announced in October that it would stop frying chicken in oils that contain trans fat. Wendy's also has banned such oils, and Burger King is testing alternatives. Arby's announced Tuesday that it would get rid of trans fat in its french fries and reduce it in other foods.

Trans fat is made when vegetable oils high in unsaturated fats are chemically modified to turn them from a liquid into a solid at room temperature. The process changes the oil's molecular structure — which health experts say results in higher bad cholesterol and lower good cholesterol and which can cause obesity, heart disease and death.

Johnson's proposal is already drawing opposition from the Kentucky Restaurant Association, which argues that a ban — especially one without a gradual phase-in — isn't necessary since many restaurants are already getting rid of trans fats. They also argue that a new law forcing them to do so before they have been able to find appropriate replacements could hurt their products and their bottom lines.

Johnson, a Democrat, said restricting trans fat is in line with the health department's mission to protect public health.

"They wouldn't let a restaurant serve rat poison, and I think this is similar to rat poison," Johnson said. "It's just a little slower in killing you."

But Council President Kevin Kramer, a Republican, said he and some other members of the Metro Council believe that Johnson's proposal gets into an area of regulating personal activity where government has no place.

Opponents argue that eliminating trans fat is not easy. Even the American Heart Association is torn on the issue.

"There is no doubt that trans fats are bad for you, but taking all trans fats out is complicated," said Julie Brackett, director of advocacy for the American Heart Association in Louisville.

The National Restaurant Association has argued in New York that a ban on trans fat could force some restaurants to turn to oils high in saturated fats, which also are unhealthy, because supplies of vegetable oils such as corn oil, canola and soybean oils are too low to meet demand if cities begin outlawing hydrogenated oils.

Laurie Schalow, a spokeswoman for KFC, said the company did tests for more than two years before settling on a special soybean oil it will now use to fry its chicken.

The plan was announced on Oct. 31, and many of KFC's restaurants are already using the new oil, but Schalow said it will be April before farmers are producing enough of the beans to supply the oil to all of KFC's 5,500 U.S. restaurants.