Cooked Meat Carcinogens

Episode 91

I know that the news today can be overwhelming–even just mentioning the word facts can trigger all sorts of reactions.  I’m Dr. Michael Greger and I happen to really like facts!  So, I’ve devoted my life to learning all there is to know about the latest nutrition research, so that you and your family can lead healthier, more productive lives.

Today, we answer some tough questions about meat.  If you or your loved ones eat meat, what is the best way to cook it? In our first story, we look at eight preparation methods to reduce exposure to carcinogens in cooked meat.

The first factor is “meat type,” with processed meat—red or white—being the worst. Then “[cooking] temperature,” cooking at under 260 degrees Fahrenheit—so, like boiling or microwaving, safer; whereas broiling, roasting, or pan-frying is the worst. “Turning [it] over” every minute lowers risk, and, rather than a “dark [and] flavorful” crust, they recommend pale and soft. Cooked rare lowers risk, as long as you meet food safety guidelines. Spices or a vinegar-containing marinade lowers carcinogen formation. Avoid gravy, stick to one serving (which is like “a deck of…cards or [the size of a] bar of soap”), and eat vegetables and fruit with your meat.

Even just being around a barbecue may be a bad idea, even if you don’t eat anything off of it.  They estimated the extra lifetime cancer risk associated with standing about six feet away from a charcoal grill every day, and about 30 feet away, with both 25% skin exposure and 100% skin exposure. They’re not talking about grilling in the nude! This is out of the recognition that light clothing probably provides little protection from these “gaseous” carcinogens. Skin “contact is often neglected in [these kinds of risk] assessments of [polycyclic aromatic hydrocarbons].” But, we know it’s a problem from studies on firefighters that show that even in “full protective” gear, breathing through a respirator, they still end up with these compounds in their bodies—likely through their neck, under their helmets.

“These results indicated that outdoor exposure to barbecue fumes (particularly [through the skin]) may have become a significant but largely neglected source of health hazards.” But, their estimates were from barbecuing once a day, every day, year-round. Though they’re thinking the toxic fumes might actually stick to people’s clothing, which they could then bring it inside with them to continue exposure.

These are all some of the chemicals that led to the official scientific body that determines what is and is not carcinogenic to declare that processed meat does cause cancer, and red meat probably causes cancer. They considered both the nitrites in processed meat, as well as these cooked-meat carcinogens. “However, due to the practically unavoidable presence of other carcinogenic compounds, which are already present in raw or unprocessed meats,…these chemicals are not the only potentially carcinogenic substances in meat and meat products. These other substances are well-known environmental pollutants, such as some heavy metals,…dioxins, and…PCBs,” so-called persistent organic pollutants, to which we’re “primarily [exposed via] dietary intake of dairy products, meat, and fish.”

How bad of a problem is this in the United States? “The…USDA…examined whether levels of dioxin-like compounds…in meat and poultry…indicate possible concern for U.S. public health,” and they concluded that “a typical U.S. adult’s daily exposure…is below the EPA-established [reference dose]”—meaning the maximum acceptable limit of a toxic substance. “Only children consuming [average] daily servings of meat or poultry…[regularly] containing the highest…levels…may exceed the [limit].”

Putting all the carcinogens together, some toxicologists suggest “limit[ing the] consumption of beef, pork, and chicken so that children…consume at most five servings [combined] of [all these] meats each month.” So, on average, like one serving every six days or so, max. Yeah, but what about organic meat? We’ll find out, next.

Researchers tested 76 samples of different kinds of meat, both organic and conventional, for 33 different carcinogens.  A study on “the carcinogenic risk associated with the intake of” various meats, estimated the risk was so great that we may not want to feed beef, pork, or chicken to kids more than like five times a month. This was in Europe, where lamb contamination is a particular problem. In the United States, if there was any standout, it would be chicken and PBDEs (flame-retardant chemicals)—not only compared to other meats, but other countries. U.S. chickens are like 10-20 times more contaminated than samples taken from other countries that have been tested—though diet is not the only source of exposure, as those eating vegetarian have only about 25% lower levels in their bloodstream than those eating meat, though a large proportion of that may be from chicken.

For other chemicals, diet may play a larger role. Studies of the “pollutants in [the] breast milk of vegetarians” dating back over 30 years have found the average vegetarian levels of some pollutants were “only 1 to 2 percent as high as the [national] average.” In fact, for the six out of seven pollutants they looked at, there wasn’t even overlap in the range of scores; “the highest vegetarian value was lower than the lowest value obtained in the [general population].” This is presumed to be because these pollutants concentrate up the food chain. So, by eating lots from all the way down the food chain—plants—those eating vegetarian may “have an edge.”

For example, dioxins. “Meat, fish, and dairy are believed to contribute almost all of the dioxin body [exposure].” And, indeed, if you look at those eating strictly plant-based diets, they may only have about a third of the levels of dioxins and PCBs, or even less than a fifth, circulating throughout their bodies.

Poor workers at these electronic waste recycling plants can be exposed to high levels of toxic chemicals, ending up with concentration of PCBs in their bloodstream—twice as high as those living about 250 miles away along the coast. But these were non-vegetarian workers at the waste plant. The PCB levels of the vegetarians working at the same plant was even lower.

The problem with these cross-sectional studies is that we can’t single out the diet. Maybe vegetarians have other lifestyle behaviors that protect them. You don’t know until you put it to the test. Change people’s diets and see what happens.

That’s hard to do with persistent pollutants like PCBs, which may take literally decades to detoxify from the body. But, we can get rid of heavy metals, like mercury, in a matter of months. And, indeed, within three months of “the exclusion of meat, poultry, fish and eggs” from their diets, there was a significant drop in the levels of toxic heavy metals in their bodies, including mercury, cadmium, and lead.” Up to about a 30% drop within three months.

What if we just stick to organic meat? Certified organic meat comes from” livestock [that are] fed with organically produced feed that is free of pesticides and animal by-products,” by law. Therefore, one would assume “that there should be [a] lower accumulation of chemical residues.” However, on a practical level, there were simply “no studies on the chemical residues’ content in organic meat”—until, now.

Researchers “acquired 76 samples of [different kinds of] meat, both organic and conventional, and “quantified their levels of contamination with 33 different carcinogenic [persistent organic pollutants].”

After all, “the ingestion of food contributes more than 90% to the total current exposure to these compounds, especially…food [of] animal origin.” “On the other hand, an increasing number of consumers” are choosing organic. In fact, “organic food production increased by 50% during the last decade.” So, are consumers of organic meat protected, or not?

Well, “no sample was completely free of carcinogenic contaminants,” which is to be expected, given how polluted our world is these days. But, what was surprising was that “the differences between organically and conventionally produced meats were minimal.” Furthermore, “the current pattern of meat consumption exceeded the maximum limits” either way.

“Strikingly, the consumption of organically produced meat [not only] does not appear to diminish this carcinogenic risk,” but was sometimes found to “be even higher.” Bottom line, sadly, is that the “[c]onsumption of organic meat does not diminish the carcinogenic potential associated with the intake of [these pollutants].”

In our final story – we explore research on viruses that may live on in meat.  As it turns out polyoma viruses discovered in meat can survive cooking and pasteurization.

“Nearly 20% of cancer[s]…can be linked to infectious agents,” such as viruses. There are seven viruses now conclusively tied to human cancers, and as new viruses enter into human populations, the incidence and causes of cancer will likely change accordingly.

The foundation of modern tumor virology was laid over a century ago, with the discovery of a cancer-causing chicken virus, for which a Nobel Prize was awarded.  Another Nobel went to the guy that discovered the HPV virus was causing cervical cancer. And in his acceptance speech, he mused that there may be a bovine polyomavirus, a multiple tumor virus, in cattle, that could be playing a role in human colon cancer, lung cancer, and breast cancer. But, no polyomavirus had ever been discovered in meat—until now.

Polyomaviruses are a particular concern, not only because they are “known to be carcinogenic,” but because they can survive cooking temperatures. Because single burgers these days can contain meat from “many dozens of animals,” they figured it would “present an ideal situation for virus-hunting.” So, researchers at the National Cancer Institute just walked into three supermarkets, and grabbed meat right off the shelf, and found three different polyomaviruses in ground beef. Now, just because three types of polyomaviruses are “commonly detectable in food-grade ground beef” doesn’t necessarily mean they are causing human disease.

What made this Nobel laureate suspect them? Well, for one thing, some people got cancer right where they were vaccinated for smallpox—a whole bunch of different cancers. The vaccine was harvested from “the…skin of calves.” And so, maybe there’s some cancer-causing cow virus?“Many people are exposed to potentially virus-contaminated meat and dairy products” through their diet, but those in the industry would be even more exposed. So, it would be interesting to see if these groups have higher cancer incidence. And, indeed, it now appears clear that those who work “in the meat industry are at increased risk of developing and dying” from a variety of cancers.

Another “reason…to suspect the involvement of [some kind of] bovine infectious factor…in colorectal cancer” is the fact that countries that don’t eat a lot of beef appear to have relatively low rates of colorectal cancer. And, countries that all of a sudden started eating lots of meat had their rates shoot up. Mongolia appears to be the exception. Lots of red meat, yet low colon cancer rates. But, “there they eat yak,” and maybe yaks don’t harbor the same viruses.

Can’t you just avoid steak tartare? Even steak cooked “medium” may not reach internal temperatures above 70 Celsius, and it takes temperatures above that to inactivate some of these viruses. So, we would expect viruses to survive both cooking and pasteurization. In fact, they followed up with a paper suggesting that consumption of dairy products may represent a “main risk factor for the development of [human] breast cancer.” The recent discovery of a larger number of presumably new viruses in the blood, meat, and milk of dairy cows should be investigated, since one might speculate that infectious “agents present in dairy products [might have a special] affinity for [breast cells],” since they came from breast cells.

The fact that people with lactose intolerance, who tend to avoid milk and dairy throughout their lives, have lower rates of breast cancer and other cancers could be seen as supporting this concept—though there are certainly other reasons dairy may increase cancer risk, such as increasing levels of the cancer-promoting growth hormone IGF-1, or adversely affecting our gut microbiome. Or, for that matter, maybe the plant-based milks they’re drinking instead could be protective. That’s the problem with population studies: you can’t tease out cause and effect. It doesn’t matter how many viruses are found in retail beef, pork, and chicken if we can’t connect the dots.  

Can’t you just look for the presence of these viruses within human tumors? They’ve tried, and found some. But, even if you don’t find any, that doesn’t necessarily mean viruses didn’t play a role. There’s this “viral hit-and-run” theory of cancer development that suggests that certain viruses can slip in and out of our DNA to initiate the cancer, but be long gone by the time the tumor matures. So, there’s still a lot of work to be done.

But, if the link between bovine polyomaviruses and human disease pans out, the National Cancer Institute researchers “envision the development of [a] high-potency…vaccine…” So, just like the HPV vaccine may prevent cervical cancer from unsafe sex, one day, perhaps, vaccines may prevent breast and colon cancer from unsafe sirloin.

To see any graphs, charts, graphics, images or studies mentioned here, please go to the Nutrition Facts podcast landing page.  There, you’ll find all the detailed information you need – plus links to all the sources we cite for each of these topics.

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