Beat the heat.
The snippets are shorthand for half a dozen potentially cancer-causing chemicals called HCAs, or heterocyclic amines, which are created when meat, poultry, and fish are cooked at high temperatures.
"We know these compounds can probably cause cancer in humans," says Elizabeth Snyderwine, Chief of the Chemical Carcinogenesis Section at the National Cancer Institute (NCI) in Bethesda, Maryland. "What we don't know yet is how significant a problem they are in the American diet."
Until there's more evidence, "it makes sense to avoid (HCAs) when we can," says Mark Knize of the Lawrence Livermore National Laboratory in Livermore, California.
How much HCAs are created depends on how long the food cooks, at what temperature, and how it's prepared.
"Meat and poultry produce the most HCAs because they contain the most amino acids and creatine, which are converted into HCAs," says Lawrence Livermore's James Felton. "Seafood produces much less, and plant foods like veggieburgers, fruits, and vegetables little or none."
Grilling, barbecuing, broiling, and pan-frying are more likely to produce HCAs than baking of roasting, because they generate more heat. A propane gas grill set on high can reach 640 [degrees] F, while a typical roasting temperature is 350 [degrees].
Cooking with liquid--boiling, steaming, poaching, or stewing, for example--generates no HCAs because the temperature never tops the boiling point of water. Ditto for microwaving, so long as the food is not overcooked or dried out.
NCI epidemiologist Rashmi Sinha says that well-done beef, pork, and chicken produce the most HCAs, particularly if they've been grilled or barbecued.
"But nowadays, with bacteria] infections, you don't want to tell people to eat rare meat," she says. "You want to cook it thoroughly, but not at a very high temperature."
(Interestingly, people who frequently eat chicken have lower rates of colon cancer. Researchers don't know why.)
While charred meat and poultry contain more HCAs, you can't always predict which meats have the most. For example:
* Fewer HCAs are found in fast-food burgers because they're cooked so quickly. "They're not exposed to the high heat over a long time that causes large amounts of I HCAs," says Knize. "There are some, but not what you get off the backyard barbecue."
* Pre-cooking or marinating cuts HCAs (see "Avoiding HCAs and PAHS").[2,3]
* Sausage casings and hot dog outer skins also seem to prevent HCAs.
* As meat and poultry shrink, they lose moisture. That pushes HCA-creating chemicals to the surface, where the heat is more intense. "If you cook the meat and it shrinks 25 to 30 percent, then you start to get higher amounts of HCAs," says Knize.
PAHs: Another Grill Menace
Whenever fat drips on a flame, heating element, or hot coals, chemicals called PAHs (polycyclic aromatic hydrocarbons) form. The PAHs waft up in the smoke and can land on the food. They can also form directly on food when it's cooked to a crisp.
"If you throw a steak or hamburger on the grill and let it get really brown--the fat's dripping off it and flames and smoke are shooting up--that's the stuff you don't want to do," says the NCI's Rashmi Sinha.
As many as 12 of the 18 PAHs found in cooked food cause cancer in laboratory animals. But proof that they cause cancer in humans is still elusive. The key to preventing PAHs: Stop the fat from dripping on the heat source (see "Avoiding HCAs and PAHs").
The Smoking Gun
People who eat more meat have a higher risk of colon and prostate cancer. Is that because they eat more saturated fat, fewer fruits and vegetables, or more or less of something else? No one knows. Could it be because they consume more HCAs and PAHs? Most research has centered on HCAs.
Only one study has asked people how much meat they ate and how they cooked it, and then waited to see who got cancer.
Among 10,000 Finns monitored for 24 years, women who reported eating the most fried meat had a 77 percent greater risk of developing cancer of the breast, endometrium, or ovary than women who ate the least. But men who ate more fried meat had no greater cancer risk than men who ate less, (The researchers didn't ask about grilled Or broiled meat.)
And six studies have found that people with breast, colon, stomach, or other cancers had eaten more fried or well-done meats than similar people without cancer.[6,7]
But being diagnosed with cancer may have biased their reporting.
Case Not Closed
"It seems very plausible that HCAs cause cancer," says Knize. "But it's still a long way from proof."
First, "the level of HCAs in food can vary by two-hundred fold or more, since it depends so much on cooking conditions," points out Lawrence Livermore's James Felton.
Second, people vary in their susceptibility. About half of all Caucasians in the U.S. inherit a slow-acting form of an enzyme called NAT2, and that makes them less susceptible to developing cancer from carcinogens like HCAs.
Put these two factors together "and you could have a thousand times greater risk of cancer than your neighbor who eats the same food," says Felton.
Lawrence Livermore has an NCI grant to work on the HCA puzzle. In the meantime, "I think we're on really safe ground to say that well-done or very-well-done meat is not good for you," says Sinha.
 New. Eng. J. Med. 323: 1664, 1990.
 Food Chem. Toxicol. 32: 897, 1994.
 Food Chem. Toxicol. 35: 433, 1997.
 Ann. Rev. Nutr. 6: 67, 1987.
 Internat. Nutr. 59: 756, 1994.
 Internat, Cancer 71: 14, 1997.
 Eur. J. Cancer Res. 2: 293, 1993.
RELATED ARTICLE: AVOIDING HCAS AND PAHs
Here's how to minimize your exposure to HCAs and PAHs. Some of the tips will also help keep harmful bacteria at bay:
WHAT TO COOK
* Use lean cuts of meat and poultry. They produce fewer PAHs because there's less fat to drip on the heating source.
* Use fish or shellfish. Most have less fat than meat, take a shorter time to cook, and seem to create fewer HCAs.
* Try tofu or veggieburgers. They produce very few or no HCAs or PAHs.
* Grill or broil vegetables or fruit. "We've never seen any of the cancer-causing compounds in grilled vegetables or fruits because the chemical precursors just aren't there," says Lawrence Livermore's James Felton.
HOW TO PREPARE IT
* Thaw frozen meat or poultry in the refrigerator before you cook it. Cooking frozen meat overexposes the surfaces to high temperatures while the inside warms up slowly.
* Cut meat and poultry into small chunks. They cook faster that way, so there's less time for HCAs to form.
* Before grilling or broiling, pre-cook meat or poultry in the microwave for two to five minutes and throw away the juice. "By discarding this juice, you can reduce HCAs by 90 percent," says Lawrence Livermore's Mark Knize.
* Marinate your meat and poultry. Marinating for even a few minutes sets up a barrier against heat that dramatically lowers the creation of HCAs. The marinade ingredients don't seem to matter, but if you're grilling, less oil means fewer PAHs because less fat drips on the coals (for recipes,). To keep bacteria from growing, keep marinating food in the fridge, and never add uncooked marinade to the cooked meat or poultry.
HOW TO COOK IT
* Try a gas grill (not set on high). It cooks at a lower temperature than charcoal or wood fires and it's easier to control the temperature.
* Use hardwood charcoal. It burns at lower temperatures than mesquite or other soft woods.
* Don't build the biggest bed of coals in your neighborhood. "Flames will increase the cooking temperature much higher than radiant heat and produce at least ten times as many HCAs," says Felton.
* Instead of spreading the coals evenly across the bottom of the barbecue, rake them to one side and cook the food on the opposite side. Or form the coals into a doughnut shape and grill over the center. "The trick is not to let flames engulf the meat and not to let the fat drip onto the coals," says Felton.
* Place the grill rack or broiler pan farther from the heat. The food will cook at a lower temperature. "Higher temperatures and overcooking seem to form more cancer-causing compounds," says Knize. If you have to cook directly over the heat source, use a drip pan to catch the juices or cover the grill rack with foil that has holes punched in it.
* Avoid eating blackened or charred food.
* Take food off the heat as soon as it's cooked. Don't put cooked food back on the same plate used for raw meat, poultry, or fish. Don't add pan drippings to sauces or basting liquids.
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|Title Annotation:||includes related article on preparing food to avoid cancer-causing agents; cancer-causing agents in cooked meats|
|Publication:||Nutrition Action Healthletter|
|Date:||Jun 1, 1998|
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