CORVALLIS, Ore. - As scientists learn more about mutagenic compounds generated during the cooking of meat - especially those with possible links to colorectal cancer - some new protective mechanisms are also emerging which may be as simple as a pot of tea or nice green, leafy salad.
According to scientists in the cancer chemoprevention program of the Linus Pauling Institute at Oregon State University, the debate is still ongoing about the mutagenic or carcinogenic effects of some of America's favorite methods of cooking meat - frying and grilling.
At least in laboratory tests, the data is disturbing. A number of cooked meat mutagens produce colon tumors in laboratory animals, and colon and rectal cancer together represent the number two cause of cancer death in the United States. Colon cancer alone will kill an estimated 47,700 people this year.
But Rod Dashwood, an associate professor and toxicologist at OSU, says his work on both the causative and protective mechanisms related to colorectal cancer points to several simple dietary alterations which, at best, may have a significant protective effect and, at worst, won't hurt anything.
"It's clearly been shown that diet is a significant contributor to many types of cancer," Dashwood said. "What we're trying to determine is how problems can be avoided with diet modification and what protective elements can be added."
Although there are clear indications that a high fat, low fiber diet is linked to a higher incidence of colon cancer, Dashwood said, there are also studies which suggest, at least with meat, that the problem may relate more specifically to how it is cooked and how much is eaten.
"Research has shown that intake levels of a class of mutagens called heterocyclic amines can be increased up to 5,000 times, depending on how meat is prepared and much you eat," Dashwood said. "The mutagens form at high temperature and with prolonged heat exposure. A popular form of cooking, over open flame on a backyard grill, is just about the worst."
However, potentially protective measures identified in Dashwood's own studies and those of other researchers include the use of cooking methods that involve lower temperatures and avoid charring. Protective dietary additions include green and black teas, foods high in chlorophyll and fiber, and possibly some vitamin supplements.
In more basic terms, that means:
- Eat only modest portions of meat, in a diet dominated by fruits, vegetables and grains.
- Cook meat low, slow, and not overly-well done, such as in a crock pot.
- Cook fish or chicken in the skin and then remove the skin before eating, not only to avoid carcinogens but also to reduce fat and calories.
- To add moisture, marinate meat before cooking, which appears to significantly reduce mutagen levels after it is cooked.
- Heat meat briefly in a microwave before cooking.
- If meat does become charred, cut off the worst parts.
- Avoid making a gravy out of meat drippings which tend to concentrate the heterocyclic amines.
- Consider adding protective foods, which can include green leafy vegetables, cruciferous vegetables such as cabbage and cauliflower, and some dairy products such as milk and cheese.
- Consider also choosing the right beverage for a healthy diet, such as green or black tea.
- Some research suggests supplements of vitamin E, selenium and long-term folate intake may play a protective role in the colon.
The dietary components of meat that may be linked to colon cancer are still under considerable scientific debate, Dashwood said. Mutagenic effects have seemed fairly profound in some laboratory studies, but less so in animal and human clinical tests. Each individual may have different, and genetically influenced, abilities to metabolize and repair DNA damage caused by mutagens.
But Dashwood said he believes that the right questions have not always been asked in human clinical studies. It's not so much whether or not meat is included in a diet, or even what type of meat is eaten, he says, but how much and how it is cooked.
"Researchers have shown that the heterocyclic amine content of a single hamburger can produce measurable changes in the DNA of exposed animals and humans," Dashwood said. "While we can't yet pinpoint exactly how much of a risk factor it is, there appears to be a correlation between colorectal cancer and high dietary levels of well-done meat."
In one of his studies, published this year in the journal Cancer Research, Dashwood and other researchers outlined molecular and genetic changes causing colon tumors in rats that had been exposed to meat-related mutagens.
In similar studies at a molecular and genetic level, Dashwood has also tried to identify dietary elements that can offset or reduce the impacts of these mutagens. Eventually, it may be possible to precisely identify the chemopreventive agents that would reduce the risk of colon and other cancers.
"We don't have all the answers yet, but we're on the right track," Dashwood said. "As a result of this research, I can honestly say that I eat more fruit and vegetables. I still eat meat, but I avoid any charred parts or remove the skin, and I try to eat more green salad before and after the meat. I also prefer healthier beverages, like tea and orange juice. These aren't huge changes, but they may be important."