Burning Issues

[Volume 104, Number 6, June 1996 - Environmental Health Perspectives]


Questions about Grilling

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

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.

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