We now know that cooking meat at high temperatures produces cancer-causing chemicals, but grilling can be made safer.
excerpted from Harvard Health Letter | June 2007
Ruining a piece of meat isn’t the only thing you need to worry about if you’re cooking at a high temperature. With heat, amino acids, the building blocks of protein, react with creatine, a compound found in muscle tissue, to form what are called heterocyclic amines. They’re produced in tiny amounts, measured in the billionths of grams. But lab and animal experiments show that heterocyclic amines have potent cancer-causing properties. The International Agency for Research on Cancer has classified several of them as possible carcinogens and one as a probable cancer-causing agent.
Meanwhile, the epidemiological evidence that frequent meat eaters stand a greater chance of getting several forms of cancer continues to grow. In 2007, studies were published that link high meat consumption to breast and kidney cancer. And late in 2006, Harvard researchers reported that high intake of red meat (beef, lamb, pork) may be a risk factor for estrogen-sensitive breast cancer among premenopausal women. Researchers have a number of possible explanations for why red meat might help cause cancer, but exposure to heterocyclic amines is a leading candidate.
Although the many epidemiological fingers point at red meat as the prime suspect, when it comes to heterocyclic amines, fish and chicken are a source just like hamburgers and steak. Fish and chicken are healthier choices than red meat, but that’s principally because of the amount and type of fat they contain.
More than the type of meat, high temperature is the crucial factor in heterocyclic amine formation. That’s why grilling, frying, and broiling are the problem: They heat meat to extremely high temperatures. Heterocyclic amines are usually concentrated in the outer few millimeters of a piece of meat closest to the heat source. Grilling is double trouble because it also exposes meat to the cancer-causing chemicals (called polycyclic aromatic hydrocarbons) contained in the smoke wafting from burning coals and any drips of fat that cause flare-ups.
How long the meat is cooked is also a factor in heterocyclic amine formation. Experiments conducted at Lawrence Livermore National Laboratory show that meat fried for 10 minutes at about 450° F contains over twice the amount of heterocyclic amines as meat fried at that temperature for just 4 minutes. At lower cooking temperatures, though, the increase isn’t as steep.
Depending on the temperature at which it’s cooked, meat roasted or baked in the oven may contain some heterocyclic amines, but it’s likely to be considerably less than in meat that has been grilled, fried, or broiled. Researchers have found high levels of the compounds in gravy made from drippings from roasted meat, so they aren’t completely absent.
As far as we can tell, nothing has been published about the heterocyclic amine content of meat cooked on indoor clamshell grills like the one promoted by boxer George Foreman. Mark Knize, a researcher at the Lawrence Livermore lab who has published a number of papers on heterocyclic amines, says when he tested meat cooked on a Foreman grill, very few heterocyclic amines were present, probably because the grill isn’t all that hot.
Marinating meat is often suggested as one way to cut down on the formation of heterocyclic amines. The thinking is that the marinade will help keep meat moist and its temperature down. In addition, perhaps some marinades imbue meat with antioxidants that offset the heterocyclic amines.
But when marinades have been put to the test in studies, the results are mixed. For example, in an experiment, Knize found that marinating chicken decreased one type of heterocyclic amine but increased another. Another study found that while teriyaki and turmeric-garlic sauces decreased heterocyclic amines in grilled steak, a barbecue sauce increased them. An Italian study published in 2007 suggested that using olive oil may reduce the colon cancer risk from eating fried meat, perhaps by cutting down on the heterocyclic amines.
Just how risky is it?
Some of the first reports about heterocyclic amines and cancer made the risk seem sky-high. One often-cited study found that women who ate hamburgers, steak, and bacon well done were over four times more likely to get breast cancer than women who consumed them rare or medium. And a 2003 study concluded that colon cancer risk almost doubled with high consumption of well-done red meat. More recent research has pegged the risk at a lower level. For example, National Cancer Institute (NCI) researchers reported in 2005 that well-done meat was associated with only a 20% increase for colorectal adenomas, the growths that precede colon cancer.
Keep in mind that the risk figures are for people who eat a lot of well-done meat. The occasional grilled hamburger or steak, even if it’s well-cooked, poses little, if any, risk.
Even if marinating isn’t the answer, techniques that let you cook meat at lower temperatures and for shorter periods of time should reduce heterocyclic amines. Here are some grilling tips from the NCI and other sources that may make grilled meat a bit safer to eat:
· Cook smaller pieces. They cook more quickly and at lower temperatures.
· Choose leaner meat Less fat should reduce the flames and therefore the smoke that contains cancer-causing agents.
Substitute more veggies. Adding more veggies to the mix is safe, healthy and delicious.
Precook it or warm it up your meat. The warmer a meat is when you start, the less time it takes to cook.The NCI says microwaving meat for two minutes before cooking it decreases heterocyclic amine content by 90%. Don’t overdo it, because microwaving can dry meat out.
· Frequent flipping. This is another suggestion from McGee for hastening cooking. He says frequent flipping means neither side has time to absorb or lose too much heat, so the meat cooks faster and outer layers end up less overdone — and presumably with fewer heterocyclic amines.