Consuming processed meats, like bacon and sausage, may increase the risk of colon cancer in humans, according to a new report by the World Health Organization, and eating unprocessed red meat may spike the chance of getting other types of cancers.
Beef jerky, bologna and their meaty cousins were dubbed Group 1 carcinogens by the WHO experts, who cited "sufficient evidence" that processed meat causes colon cancer.
Tobacco, asbestos and formaldehyde also fall into Group 1.
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Fresh red meat, like beef or lamb, was dubbed a Group 2A carcinogen, or "probably carcinogenic to humans." Other substances in this category include glyphosate, which is found in many commercial weedkillers, and ultraviolet radiation.
"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," said WHO expert Kurt Straif, reports the New York Times. "In view of the large number of people who consume processed meat, the global impact on cancer incidence is of public health importance."
The formal review tallied data from 800 studies that looked at the relationship between meat consumption and over a dozen different cancers. The conclusion: eating 50 grams of processed meat each day increases colon cancer risk by 18 percent.
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Fifty grams isn't that much: It equals roughly 1.5 ounces.
Why is processed meat so dangerous?
Carcinogens are most likely introduced in processed meats during the actual act of processing, including curing, smoking or grilling.
Here's what happens: Compounds called heterocyclic amines (HCAs) and polycyclic aromatic hydrocarbons (PAHs) are formed when meats come in contact with high temperatures. HCAs and PAHs have been shown to change human DNA in ways that set the stage for cancer, according to the National Cancer Institute (NCI).
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PAHs develop when fat and juices from the meat drip down onto the open flame, reacting with the fire and causing flames that contain PAH. The PAH then sticks to the meat. (This can also happen when meats are smoked.)
HCAs develop when the different macronutrients in meats react with each other when exposed to high temps.
Grilling or pan frying meat over 300 degrees will trigger HCAs, and the longer you grill or fry, the more HCAs develop. PAHs appear anytime a meat is charred.
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Previous large-scale epidemiological studies have shown a link between diets high in well-done, fried and barbecued meats and colon, pancreatic and colon cancer, adds NCI.
Is some meat okay?
The case against fresh red meat, however, is more complicated than the WHO report implies.
For one, the nutritional profile of meat is almost completely dependent on what the animal has eaten during its lifespan.
"Grass-fed, pastured beef and grain-fed beef are so vastly different in their nutritional values, that they cannot realistically be considered the same food source," writes oncologist Colin Champ.
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Meat from animals that have been grass-fed are rich in inflammation-cooling omega-3 fats. They're also higher in conjugated linoleic acid (CLA), a substance that has been shown to confer a protective property against cancer, reports the Mayo Clinic.
There is significantly less CLA in grain-fed beef, and significantly more inflammation-promoting (and thereby cancer-promoting) omega-6 fats.
What's more, noted the WHO experts, "no clear association was seen in several of the high quality studies" between fresh red meat consumption and cancer risk, reports the Wall Street Journal. They also pointed out how tricky it was to control for other factors, like smoking or physical inactivity, that can play a role in cancer risk.
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The best advice for concerned meat eaters might be to heed the familiar mantra: "Consider the source."
"The nutritional benefit (or detrimental effect) of a hotdog full of processed meat and nitrates is NOT THE SAME as grass-fed beef," continued Champ. "All meat is not created equal, so to study industrially produced meat products and apply that data to free-range, grass-fed meat is scientifically false."
Those who are considering cutting down on meat in light of the findings might adopt a slightly altered mantra: "Consider the alternative." Replacing meat with heaps of sugary candy might be equally as damaging. Replacing it with vegetables will do a body good.