Thursday, September 24, 2015

Real Deal #11: Why Grilling Meat At High Temperatures Can Be Carcinogenic

The risk of getting cancer from occasional grilling is "very, very low," adds Dr. Pariza. He adds there's a bigger risk of food poisoning so it's important to cook meat thoroughly to avoid poisoning from E.coli and salmonella.


Cooking meats with charcoal or gas grills can cause the formation of compounds called heterocyclic amines (HCAs) and polycyclic aromatic hydrocarbons (PAHs). HCAs are formed in muscle meats cooked at high temperatures (like red meat, poultry and fish). These can cause changes in the eater's genetic material that may increase the risk of cancer, according to the National Cancer Institute. PAHs are carcinogenic substances formed when fat and juices from meats drip onto a fire, causing flames that coat the food above with PAHs. PAHs can also be formed in smoke from charcoal or wood pellets, scientists say. Exposure to some PAHs is known to cause skin, liver, stomach, and several other types of cancer in lab animals.

Cooking at high heat can produce a chemical reaction between the fat and protein in meat, creating toxins called advanced glycation end products, or AGEs. These toxins are linked to the imbalance of antioxidants in the body (aka oxidant stress), along with inflammation, which can lead to an increased risk of diabetes and cardiovascular disease. AGEs are created through a nonenzymatic reaction between reducing sugars and free amino groups of proteins, lipids, or nucleic acids. This reaction is also known as the Maillard or browning reaction.


The evidence linking cancer to cooking meat over a combustion source has been accumulating for decades. Epidemiologists first noticed a connection between the consumption of smoked foods and stomach cancer in the 1960s. Japan, Russia, and Eastern Europe, where smoking is a popular way to preserve meat and fish, became laboratories for gastric cancer research. Newer studies suggest that eating smoked meats may lead to cancer even outside the gastrointestinal tract. A 2012 study, for example, linked smoked meat consumption with breast cancer.

In subsequent decades, it has become clear that smoking isn’t the only problematic cooking method. Frying bacon, for example, produces significant levels of PAHs, probably due to volatilization of carbon in the bacon itself. An Iranian study published last year found that people who develop certain kinds of gastrointestinal cancers are more likely to have a diet high in fried rather than boiled foods. (The researchers linked level of browning to cancer incidence, thus reducing the likelihood that oil consumption was the culprit.) The FDA and WHO also remain concerned about the presence in food of acrylamides, a known carcinogen that forms from sugar and amino acids when cooked at high temperatures. Long-term studies are currently underway. The worrying implication is that cooking foods at high heat, even without active combustion, may be dangerous.

Studies have found a connection between HCAs and prostate, pancreatic, and colorectal cancer in adults.

When food is burned, these chemicals stack up, so remove all charred or burned bits before eating, too.

Epidemiological studies link occupational exposure to PAHs to cancer in humans. When PAHs from a flame mingle with nitrogen, say from a slab of meat, they can form nitrated PAHs, or NPAHs. NPAHs are even more carcinogenic than PAHs in laboratory experiments.

This study found that the direct mutagenicity of the NPAHs with one nitrogen group can increase 6 to 432 times more than the parent compound. NPAHs based on two nitrogen groups can be 272 to 467 times more mutagenic. Mutagens are chemicals that can cause DNA damage in cells that in turn can cause cancer. The findings were published in December in Environmental Science and Technology, a professional journal.

The formation of AGEs is a part of normal metabolism, but if excessively high levels of AGEs are reached in tissues and the circulation they can become pathogenic. The pathologic effects of AGEs are related to their ability to promote oxidative stress and inflammation by binding with cell surface receptors or cross-linking with body proteins, altering their structure and function. AGEs are also naturally present in uncooked animal-derived foods, and cooking results in the formation of new AGEs within these foods. In particular, grilling, broiling, roasting, searing, and frying propagate and accelerate new AGE formation.

A 2003 report from researchers at Rice University, in Houston, Texas, found that grilling creates "ambient fine particulate matter"--air pollution, in other words. Although backyard barbecues add far less pollution to the atmosphere than cars and factories, this particulate matter can still cause problems. In concentrated amounts, the smoke from a grill can trigger respiratory trouble in people with lung diseases such as asthma or chronic obstructive pulmonary disease (COPD).

Paul Billings, the vice president of advocacy at the American Lung Association, recommends cooking over natural gas or propane grills to reduce the pollution emitted. If you own a charcoal grill, using a chimney starter instead of lighter fluid will also keep you from inhaling harmful chemicals, he says.

Kristie Sullivan, a toxicologist at the Physicians Committee for Responsible Medicine, a Washington, D.C., nonprofit that includes the Cancer Project, says it is true that one source of carcinogens is eliminated if smoke doesn't come up from the heat source and onto the meat. But Ms. Sullivan says HCAs are formed by a combination of time and amount of heat, and that there's no way to know if a wood-pellet grill forms less without doing very expensive testing. While the public's image is of charred meat as cancer causing, in fact carcinogenic chemicals can be formed without visible burning, she adds.

Researchers say there is a possibility that smoke from wood pellets could contain PAHs. Hardwoods tend to burn cleanly. But "if nobody's analyzed the smoke, it's all guesswork," says Michael Pariza, a scientist at the Food Research Institute at the University of Wisconsin in Madison.


So, should you throw your charcoal grill away and bring out the Crock-Pot this Memorial Day weekend? The evidence to support such a move may not be there—yet. The EPA is developing relative potency factors to define the cancer risk of exposure to PAHs, but it’s difficult to clearly define the carcinogenicity of an activity like grilling and eating a steak. Blasting genetically-streamlined animals with carcinogens in a laboratory environment is easy enough, but human exposures to PAHs are complicated by differences in ventilation and cooking temperatures, among other variables, and the effect of PAHs is almost certainly mediated by factors such as other foods in the diet and genetic diversity.

1. Grill Fruits and Vegetables
PAHs and HCAs don't form on grilled fruits and vegetables. Plus, if you are having grilled meat, it's a great idea to get antioxidant-rich fruits and vegetables in the same meal. Try eating grilled meats with cruciferous vegetables (like broccoli). These superfoods contain fancy anti-inflammatory nutrients called isothiocyanates that change the way the body breaks down dangerous grilling chemicals, making the meat safer.

2. Grill Smart, Grill Lean
When you're grilling meat, limit the amount of fat that drips on the coals by starting with lean cuts trimmed of visible fat and skin. Fish and chicken also have lower levels of the amino acids that lead to HCA production, says Colleen Doyle, MS, RD, the director of nutrition and physical activity for the American Cancer Society. Removing the skin from chicken can help reduce the risk as well, Reader's Digest reported.

3. Marinate!
Use fat-free or low-fat marinades on your grilled meats, fish, and poultry to limit the fat that drips on the coals. The simple act of marinating before grilling has been shown to reduce the formation of HCAs by as much as 92% to 99% in some studies. Meats and poultry should marinate at least 1-2 hours; fish and vegetables generally only need to marinate for an hour.

One study showed that adding spices, such as thyme, sage, and garlic, can reduce the amount of total HCAs by 60% compared to the control. Rosemary may be especially potent - a 2008 study found that high concentrations of rosemary extracts may reduce HCAs by up to 90% in some cases.

4. Cut Down on Grilling Time
Grill smaller portions of meat, poultry, and fish so they cook faster and spend less time on the grill. A fun way to cut down on grilling time is to thread small pieces of meat or fish on a skewer. Or allow some extra time, and try to cook your meat below 325°F, which is the temperature at which HCAs begin to form.

5. Microwave
This gets the HCAs out of the meat and into the juice, which you should throw out. "Then you can cook it really well done and have no HCAs," said James Felton, associate director of the University of California, Davis Cancer Center. Precooking a hamburger for a few minutes in the microwave reduces HCAs by up to 95 percent.

6. Flip It!
Flipping food frequently may help prevent the formation of HCAs, according to recent research using hamburger patties. To turn meat without piercing it (which releases juices that drip onto the coals), use tongs or spatulas instead of a fork. To prevent cooking at temps too high, use a thermometer to regulate how hot the grill gets. Steak should be cooked to 145 degrees F, hamburgers at 160 degrees, and chicken at 165 degrees.

More information:
» Reader's Digest: "7 Guidelines for Healthier Grilling"
» Huffington Post: "Cooking with Charcoal vs. Gas: The Definitive Answer"

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