A startling report by an international team of scientists suggests that processed meats like hotdogs and bacon are a definite cause of cancer, while red meat is a probable cause. Here’s what this means to your health and why you have no reason to panic.

Eating processed meats like hotdogs, sausages, and bacon causes bowel cancer, while the consumption of red meats, including beef, pork, veal, and lamb, is probably carcinogenic, an international team of experts has concluded. They evaluated over 800 studies analyzing associations between more than a dozen forms of cancer with the consumption of processed or red meat in different countries and among populations with diverse diets.

That conclusion is causing considerable consternation and a rethink of what a healthy diet is supposed to look like. The Washington Post is calling it “one of the most aggressive stances against meat yet taken by a major health organization,” adding that it’s “expected to face stiff criticism in the United States.” No doubt, it’s an important report, but health experts say that we shouldn’t exaggerate the extent of the findings, or rush to completely eliminate red and processed meats from our diets altogether.

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Definite and Probable Causes

Back in 2014, an international advisory committee listed the effects of consuming processed and red meats as a high priority study area for the World Health Organization’s International Agency for Research on Cancer (IARC) Monographs program. It’s well known that certain meats have an association with cancer; in this respect, the latest report, which now appears at The Lancet, offers very little that is new. It merely brought the existing literature together in a way that finally allowed scientists to make some definite proclamations about the cancer risks of eating processed and red meats.

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After sifting through decades’ worth of scientific literature, an IARC working group of 22 experts from 10 countries classified the consumption of processed meat as a Group 1 carcinogen to humans (processed meats are defined as meats that have been transformed through salting, curing, fermentation, smoking, or other processes to enhance flavour or improve preservation). This conclusion was reached on “sufficient evidence” that the consumption of processed meat causes bowel, or colorectal, cancer.

Other forms of cancer, such as stomach and pancreatic cancers, have also been linked to certain meats, though these associations have been more difficult to prove. The IARC group categorized red meat as a Group 2A probable carcinogen to humans based on the “limited evidence” showing that the consumption of red meat causes cancers in humans.

When the researchers say that there’s sufficient evidence, they’re claiming that there’s enough convincing evidence to show that these types of meats actually cause cancer—evidence gleaned from animal experiments, studies of human diet and health, and so-called mechanical causes, such as cell mechanisms, of cancer. As for the limited evidence showing that red meat is probably carcinogenic to humans, the researchers are saying that a positive association has been observed as it relates to the onset of colorectal cancer.

As noted in The Washington Post, the report will “likely play out with political lobbying, and in marketing messages for consumers,” but negative reactions to the report also shows how difficult it is for scientists to link any food to a chronic disease:

Experiments to test whether a food causes cancer pose a massive logistical challenge - they require controlling the diets of thousands of test subjects over a course of many years. For example, one group would be assigned to eat lots of meat, and another less, or none. But for a variety of reasons involving cost and finding test subjects, such experiments are rarely done, and scientists instead often use other less direct methods, known as epidemiological or observational studies, to draw their conclusions.

“I understand that people may be skeptical about this report on meat because the experimental data is not terribly strong,” said Paolo Boffetta, a professor of Tisch Cancer Institute at the Mount Sinai School of Medicine who has served on similar WHO panels. “But in this case the epidemiological evidence is very strong.”

Other scientists, however, have criticized the epidemiological studies for too often reaching “false positives,” that is, concluding that something causes cancer when it doesn’t.

The report will be subject to considerable scrutiny over the coming weeks and months.

Understanding the Risk

“For an individual, the risk of developing colorectal cancer because of their consumption of processed meat remains small, but this risk increases with the amount of meat consumed,” noted Kurt Straif, Head of the IARC Monographs Programme, in a statement. “In view of the large number of people who consume processed meat, the global impact on cancer incidence is of public health importance.”

Specifically, the researchers say that risk of colorectal cancer increases by as much as 18% with each 50 gram (1.8 ounce) portion of processed meat eaten daily, and increases by some 17% with each 100 grams (3.5 ounces) of red meat consumption. But it’s important to keep these figures in perspective. Writing at Cancer Research UK, Casey Dunlop explains:

Remember these are all ball-park figures – everyone’s risk will be different as there are many different factors at play.

We know that, out of every 1000 people in the UK, about 61 will develop bowel cancer at some point in their lives. Those who eat the lowest amount of processed meat are likely to have a lower lifetime risk than the rest of the population (about 56 cases per 1000 low meat-eaters).

If this is correct, the WCRF’s analysis suggests that, among 1000 people who eat the most processed meat, you’d expect 66 to develop bowel cancer at some point in their lives – 10 more than the group who eat the least processed meat.

Tobacco smoking and asbestos are also classified as Group 1 carcinogens, but that doesn’t mean—as this Guardian article falsely suggests—that processed meats are as carcinogenic as those agents. Rather, the IARC classifications merely describe the strength of the scientific evidence as it pertains to a possible cause of cancer. Yes, processed meats and smoking both cause cancer, but to dramatically different degrees.

Recent estimates suggest that, around the world, 34,000 cancer deaths can be attributed to diets high in processed meat each year. Diets high in red meat, which has not been positively linked as a direct cause of cancer, could be responsible for as many as 50,000 deaths per year worldwide, though it’s difficult to know exactly. By contrast, smoking causes about a million deaths per year, while alcohol consumption results in about 600,000 deaths each year globally.

As to why certain meats cause cancer, here’s what the IARC has to say:

Meat consists of multiple components, such as haem iron. Meat can also contain chemicals that form during meat processing or cooking. For instance, carcinogenic chemicals that form during meat processing include N-nitroso compounds and polycyclic aromatic hydrocarbons. Cooking of red meat or processed meat also produces heterocyclic aromatic amines as well as other chemicals including polycyclic aromatic hydrocarbons, which are also found in other foods and in air pollution. Some of these chemicals are known or suspected carcinogens, but despite this knowledge it is not yet fully understood how cancer risk is increased by red meat or processed meat.

The jury is still out on red meat, and its carcogenic effects likely have something to do with how it’s cooked.

How Much Meat to Eat?

So what does all this mean in terms of adjusting our meat-eating habits?

“These findings further support current public health recommendations to limit intake of meat,” says IARC Director Christopher Wild. “At the same time, red meat has nutritional value. Therefore, these results are important in enabling governments and international regulatory agencies to conduct risk assessments, in order to balance the risks and benefits of eating red meat and processed meat and to provide the best possible dietary recommendations.”

It’s an admonition that’s echoed by many health and diet experts, including physician David Wallinga from the University of Minnesota:

These are WHO’s two highest cancer classifications. The risk rises with the amount of meat consumed. It would not be good medicine to wait longer before strongly advising the public to eat less red meat and especially less processed meat. WHO recommendations also include eating diets higher in whole grains and vegetables, in addition to limiting red and processed meats, because of evidence that dietary fiber protects against cancer.

Luckily, the WHO’s ruling comes on the heels of a growing trend toward eating less and better meat in America. American red meat consumption has already dropped about 25% since the mid-1970’s. But Americans on average still eat about 1.9 lbs of red meat per week - approaching double the E.U.-recommended amount of no more than about 500 grams (1.1 lbs) of cooked red meat per week.

Wallinga says that we should eat less and better meat.

Dunlop says that red and processed meat still have a place in a healthy diet. “Regularly eating large amounts of red and processed meat, over a long period of time, is probably not the best approach if you’re aiming to live a long and healthy life,” he said. However, “Meat is fine in moderation—it’s a good source of some nutrients such as protein, iron and zinc. It’s just about being sensible, and not eating too much, too often.”

Dunlop points to a government report advising people who eat more than 90g (3.2 ounces) (cooked weight) of red and/or processed meat a day to cut it down to 70g (2.5 ounces) or less.

Credit: Cancer Research UK

It’s also a good idea to substitute these meats with chicken, turkey, or fish, while adding more fibre, fruit, and vegetables. And given the detrimental impacts of raising livestock on the environment, not to mention the intense suffering endured by factory farmed animals, it’s also worth considering a vegetarian or vegan diet.

Read the entire study at The Lancet: “Carcinogenicity of consumption of red and processed meat”.

[ Washington Post | NRDC Switchboard | Cancer Research UK ]


Email the author at george@gizmodo.com and follow him at @dvorsky. Top image by stux/pixabay/public domain