sealPurdue News

March 1996

Cheeseburgers rich in cancer-fighting compound

WEST LAFAYETTE, Ind. -- There's a flip side to the cheeseburger's reputation as a greasy, artery-clogging, cancer-causing meal. Would you believe it's a prime source of a cancer-fighting compound?

It's true. Research by Martha Belury, assistant professor of foods and nutrition at Purdue University, has found that a polyunsaturated fatty acid called conjugated dienoic linoleic acid (CLA) can inhibit skin cancer in mice. In this study Belury also found that CLA can inhibit skin cancer during more than one of the three stages of disease development. Her work was published in the journal Nutrition Reviews.

Other researchers who first noticed CLA in fatty fried hamburger have found the largest amounts of CLA in ruminant meat, cheese, and processed cheese. They've also found some in milk and yogurt, less in poultry, eggs and corn oil. Heating food, like pan-frying meat or pasteurizing milk, increases the CLA content.

Working with funding from the National Livestock and Meat Board, Belury fed CLA to cancer-prone test mice. The mice developed fewer skin tumors than did similar mice not fed CLA. Other researchers have shown that CLA inhibits mammary cancer in rats and stomach cancer in mice.

Most cancer-fighting compounds that have been found in food affect only one organ, such as the stomach or skin or colon, Belury says. "The fact that CLA protects against stomach, mammary, and skin cancers makes it unique," she says. "It's an indicator that something is going on here."

That "something" is a puzzle with several pieces still missing. Belury added yet another puzzle piece when she found that CLA inhibits cancer during more than one of its three stages of development.

Cancer progresses through these stages: initiation, when a cell or cells are genetically damaged to become precancerous; promotion, when precancerous cells multiply to form tumors; and progression, when tumors enlarge and spread to other organs.

Before Belury's work, other researchers showed that CLA can inhibit cancer during initiation. When Belury conducted tests on already initiated, precancerous cells, she found that CLA also halted the multiplication of precancerous cells during the promotion stage. That's important because promotion is the longest-lasting stage in the development of cancer -- the stage where diet makes the most difference.

Researchers still puzzle over exactly how CLA inhibits cancer during any stage of the disease, but laboratory tests have given some clues. In certain tests, CLA acts as an antioxidant that stops harmful molecules called free radicals from damaging cells in ways that could cause cancer. Other laboratory tests suggest that CLA might selectively kill cancer cells, or that it might replace other, cancer-promoting fatty acids in the cell membrane.

Belury still doesn't know if CLA will work against cancer in people, but she argues that results of current tests warrant human clinical trials. If it does fight cancer in humans, CLA might easily be worked into peoples' diets, because it doesn't take huge doses of CLA to have an effect, Belury says.

She stresses that her findings don't contradict the National Cancer Institute's recommendation that people cut down on total fat intake. It's still important to reduce fat intake, Belury says, because diet does affect people's chances of developing health problems such as heart disease and cancer. Epidemiologists estimate that diet is a contributing factor in 35 percent of cancer deaths in the United States.

However, Belury and others have found that the relationship between dietary fat and cancer isn't simple and one-sided.

Source: Martha Belury, (765) 494-0302; Internet,
Writer: Rebecca J. Goetz, (765) 494-0461; Internet,
Purdue News Service: (765) 494-2096; e-mail,

NOTE TO JOURNALISTS: Copies of the article in Nutrition Reviews are available from Rebecca J. Goetz, (765) 494-0461. Color photo of a cheeseburger and black-and-white photo of Martha Belury available from Purdue News Service, (765) 494-2096.

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