A nutrition advocacy group sued Burger King Holdings Inc. Wednesday over the hamburger chain's use of frying oil that contains artery-clogging trans fats.

In court papers filed in Washington, D.C. superior court, the Center for Science in the Public Interest said Burger King is the only leading restaurant chain that has not yet committed to eliminating trans fats from its menu.

"Burger King not only sells food cooked with this harmful ingredient, it does so without warning its customers about life-threatening consequences," the suit said. "Consumers have no way to guard against the risk of consumer trans fats."

Trans fat increases the low-density lipoprotein -- so-called bad cholesterol -- in food, and U.S. health officials have advised Americans to consume as little trans fat as possible.

Restaurants are not legally required to disclose the amount of trans fat in their foods, but CSPI attorney Stephen Gardner said the risks associated with eating trans fats make the products unsafe.

"Given the current state of knowledge... the deliberate use of trans fat, which is completely nonessential, makes those foods deleterious," Gardner said.

Burger King (Charts) spokesman Keva Silversmith said the company was "disappointed that CSPI elected to bring this baseless lawsuit" and said the company was "committed to eliminating trans fats from its products."

The world's No. 2 hamburger chain is currently testing a variety of healthier oils in hundreds of restaurants in five U.S. markets, Silversmith said. He declined to specify which markets.

Depending on which oil the company decides to use, a nationwide switch to a healthier oil could happen as soon as late 2007, Silversmith said. However, if another oil is selected, the roll-out may not be completed until the end of 2008, he added.

The decision on which oil to use will be based on how the products taste to consumers as well as supply and operational issues, Silversmith said.

Several chains, including Wendy's International Inc (up $0.22 to $39.23, Charts)., Yum Brands Inc.'s (up $0.59 to $66.22, Charts, Fortune 500) KFC and Taco Bell units, Starbucks Corp. (down $0.22 to $28.20, Charts, Fortune 500) and McDonald's Corp. (up $0.70 to $51.97, Charts, Fortune 500) have either already made the switch to healthier oils or have said they are working on replacing oils they currently use.

Last June, CSPI and a Washington law firm sued Yum Brands to force it to eliminate trans fats from food at its KFC fried chicken chain. In October, KFC said it would switch to a cooking oil with no trans fat and CSPI withdrew from the suit.

The suit, however, continued, and was dismissed by a federal judge earlier this month.

Both New York City and Philadelphia in recent months banned artificial trans fats from restaurants. New York's ban goes into effect this summer. Philadelphia's ban will be phased in over the next 18 months.

Burger King shares edged down 20 cents, or 0.8 percent, to $25.20 in early-afternoon trade.