November 28, 1998

Very hot grills may inflame cancer risks

By J. Raloff

Women who consistently eat their meat very well done—with a crispy, blackened crust—face almost five times the breast-cancer risk of those who eat rare- or medium-cooked meats, a new study finds. However, even well-done meats without char may contain the chemicals being linked to this cancer risk, a pair of related analyses indicates.

The new studies suggest that how people cook meats can have major health implications.

For years, scientists have been investigating the conditions under which a family of carcinogens known as heterocyclic amines (HCAs) develop in cooked meats. Test-tube studies have shown that several HCAs can bind to DNA in breast cells, forming molecular structures called adducts, a first step in cancer development. Whether such adducts appear and provoke cancer in people, however, has remained uncertain.

Now, a group from two midwestern universities and the National Cancer Institute in Bethesda, Md., find strong support for the link between HCAs and cancer. They compared the eating habits of 273 participants in the Iowa Women’s Health Study who developed breast cancer between 1992 and 1994 with the preferences of 657 women who remained cancerfree. Women who consistently ate meats very well done proved 4.6 times as likely to have the cancer as those who ate meats rare or medium.

Even accounting for other cancer risks, such as a family history of this disease, use of hormone supplements, or a high waist-to-hip ratio, meat-doneness preference remained an independent predisposing factor, the scientists report in the Nov. 18 Journal of the National Cancer Institute. These data "strongly suggest that HCAs and possibly other compounds formed during high-temperature cooking may be breast carcinogens in humans," they conclude.

"If these findings are confirmed," says study leader Wei Zheng, an epidemiologist now at the University of South Carolina School of Public Health in Columbia, "this could be very important for breast-cancer prevention" by pointing to an easily modified dietary risk.

Exploring conditions that foster HCAs, researchers at Lawrence Livermore (Calif.) National Laboratory (LLNL) showed that meats must be subjected to high temperatures for relatively long periods (SN: 4/23/94, p. 264). That’s why blackening the exterior of a rare steak with a flash searing leaves meat relatively free of HCAs, as does precooking it at relatively low temperatures in the microwave and then browning the surface quickly in a broiler.

In a new analysis, the LLNL team quantified HCAs in spare ribs, steaks, hamburgers, and chicken cooked to order in sit-down restaurants. In the November Journal of Agricultural and Food Chemistry, they report that in general, the more well done the meat, the more HCAs it contains.

In the samples that were the most well done, HCAs laced beef at 5 to 10 parts per billion. This was almost 10 times the concentrations seen in meats cooked to the same doneness in the researchers’ lab, observes study leader Mark G. Knize, and more than 100 times those found 3 years ago in fast-food burgers.

J. Scott Smith and Basira G. Abdulkarim of Kansas State University in Manhattan present related data in the same issue. They compared HCAs in processed meats, like bologna and smoked sausage, with those in fresh-cooked beef. They found no detectable HCAs in most of the sausages—until they were fried. "And that’s not surprising," Smith says, because such meats are manufactured at low temperatures.

Fat content can also prove important. When fried under the same conditions, hamburgers that started with 5 percent fat developed up to five times the concentrations of HCAs as burgers starting with 15 percent fat. The reason, Smith suspects, is that the fat has an insulating effect.

While the new data offer health-conscious cooks some food for thought, they also are prompting a genetic probe. Not all people make equal amounts of the enzymes that activate HCAs. Zheng plans to study whether those who make the greatest amounts of enzymes face the highest cancer risks from well-done meats.

From Science News, Vol. 154, No. 22, November 28, 1998, p. 341. Copyright © 1998 by Science Service.