Accompanying each savory morsel of charbroiled meat are cancer-causing heterocyclic amines (HCAs). New studies indicate that HCAs may be involved in diseases such as cardiomyopathy, mammary cancers, and colon cancer. Even the fumes of cooked meats contain HCAs, which may pose respiratory risks for those who don't eat meat.
HCAs, formed during cooking when naturally occurring amino acids in meat react with muscle creatine, are among the most potent mutagens and carcinogens known. In a recent study completed at York University in London and the Lawrence Livermore National Laboratory (LLNL) in Livermore, California, when patients scheduled for colon surgery were given trace doses of radiolabelled HCAs (equivalent to the amount in four well-cooked, quarter-pound hamburgers) beforehand, minute amounts were recovered from DNA in the tissue removed during surgery. "Even at these small levels, the carcinogen binds to DNA, showing how powerful it is," said Mark Knize, a biomedical scientist at the LLNL.
Early investigations of the health risks of HCAs have focused on ingestion as the primary route of human exposure and the colon as the primary target. Recent animal studies suggest that HCAs target other organs as well. In rats, HCAs trigger cardiomyopathy, the inflammation and deterioration of heart tissue that occurs with age. The primary cause of human cardiomyopathy remains unknown, but, "dietary factors like HCAs may play a role," says Elizabeth Snyderwine, chief of the Chemical Carcinogenesis Section at the National Cancer Institute.
Snyderwine and colleagues Richard Adamson and Unnur Thorgeirsson noticed that monkeys with HCA-induced liver cancer also developed an unexpectedly high incidence of degenerative heart damage. When they gave HCAs to adult rats (100 milligram per kilogram per day by gavage for two weeks) and cultured rat myocytes (200 micromolars for two hours), both experiments caused abnormal mitochondria, loss of myofilaments, and cell death. Studies in human cell lines and epidemiological evidence are needed to determine whether HCAs contribute to human cardiomyopathy.
Snyderwine's team also found that HCAs target the mammary glands of rats and are passed to their offspring through nursing. A study published in the 20 July 1994 issue of the Journal of the National Cancer Institute showed that when lactating rats were fed a single oral dose of 10 mg/kg of HCAs, metabolites showed up in the urine of nursing, five-day-old rat pups. "This might be a model for the human situation," says Snyderwine. Humans are continuously exposed, starting early in life, to low doses of carcinogens like HCAs, which are promoted, not just later but early on as well, by factors like dietary fat to produce cancer. However, it's too early to say that eating meat and breast feeding don't mix. Antioxidants and other nutrients may counteract HCAs, and no investigation has been done in humans.
Because epidemiological studies (cited in the July 1994 issue of the Journal of Agricultural and Food Chemistry) find an increased risk of respiratory tract cancers among cooks, researchers at the LLNL analyzed the amount of HCAs produced by frying beef hamburgers, bacon, and soy-based tempeh burgers. The results, published in the October 1995 issue of Food Chemistry and Toxicology, showed the total HCAs in the smoke condensate were 3 nanograms per gram (ng/g) from bacon and 0.37 ng/g from hamburgers, compared with 163 ng/g in cooked bacon and 110 ng/g in cooked beef. Levels of HCAs in tempeh, which lacks creatine, were nondetectable.
Airborne HCAs present the greatest risk to professional cooks who stand over a stove all day, says Knize. A fume hood could decrease the risk. For home cooks, eating meat, rather than breathing in the cooking fumes, poses the greatest hazard.
The consumption of HCAs in the United States averages 26 ng/kg/day. "The amounts are small, compared to other pollutants," says Knize, "but [HCAs] are powerful mutagens and carcinogens." And the recent culinary trend to switch from beef to chicken may not be quite so healthy when it comes to HCAs. In his study in the 15 October 1995 issue of Cancer Research, Knize found that pan-fried, oven-broiled, and grilled chicken contain two- to seven-fold more HCAs than fried beef.
Meat connoisseurs can lessen their intake by cutting away the HCA-rich char that forms during cooking. Reducing cooking temperatures helps, too. The LLNL researchers found that beef cooked at 198¡ C and 277¡ C contained 10.5 ng/g and 110 ng/g of HCAs, respectively.
A new grill, invented by microbiologist Richard Basel at Lebensmittel Consulting in Fostoria, Ohio, allows people to enjoy grilled meats without the carcinogens. Named the Safe Grill, it blocks both HCAs and polyaromatic hydrocarbons, which form when fat drips into the fire. A special filter placed between the fire and the meat blocks carcinogens from rising and coating the meat. The filter contains special fractionation packing that separates the desirable lower-boiling-point flavor compounds from the undesirable higher-boiling-point carcinogenic compounds, allowing only the desirable flavor compounds to pass through.
In addition, the Safe Grill cooks meat at a lower temperature, which prevents flames from directly charring the meat. Taste panels judged meats cooked on the Safe Grill to be more flavorful and tender than those cooked on conventional grills. The invention of the Safe Grill was funded by National Cancer Institute to reduce the threat of cancer from foods.