A scientist found cancer-fighting fatty chemicals in cheese and grilled ground beef but says it's no excuse to go stuff yourself on cheeseburgers.

"People should be reassured to know there are things in food that prevent cancer," said microbiologist Michael Pariza, who conducted the research as director of the University of Wisconsin's food safety research institute.But saturated fats and cholesterol also found in beef and cheese have been linked previously to heart disease and some cancers.

So "we're certainly not suggesting that people go out and chow down on cheese and hamburgers," Pariza said Tuesday during the American Cancer Society's science writers' seminar.

He said fears of cancer-causing substances in food were aggravated by recent reports of Alar in apples and aflatoxin in grain, as well as a 1986 Lawrence Livermore National Laboratory study that found well-done fried and broiled hamburgers contain chemicals that cause cancer and mutations in rodents.

Pariza said his findings show that "in many foods there are good substances that may counteract the effect of bad substances."

His study found varying amounts of the cancer-inhibiting fatty acids - called CLA, or conjugated linoleic acids - in hamburger and natural and processed cheeses. Highest levels were in Cheese Whiz sandwich spread, followed by grilled hamburger.