The WHO’s cancer agency, in a decision certain to intensify the debate over the American diet, classified processed meat as “carcinogenic to humans” and red meat as “probably carcinogenic to humans.” The International Agency for Cancer Research rating of processed meat, such as cured and smoked products, is its strongest categorization of evidence that an agent is capable of causing cancer; the classification for red meat — which covers raw beef, pork, mutton, horse or goat meat — is the second-strongest on a five-point scale. The IARC reported its decision in the journal The Lancet Oncology.
The meat industry, which had braced for months for an adverse report, faulted IARC for a “dramatic and alarmist over-reach” that did not consider the benefits to human health of meat consumption. The North American Meat Institute said IARC’s panel of 22 scientists from 10 countries “tortured the data to ensure a specific outcome.”
In The Lancet Oncology, IARC said the working group assessed more than 800 epidemiological studies with the clearest evidence related to meat and colorectal cancer.
“Overall, the Working Group classified consumption of processed meat as ‘carcinogenic to humans’ on the basis of sufficient evidence for colorectal cancer. Additionally, a positive association with the consumption of processed meat was found for stomach cancer,” said the article.
“The Working Group classified consumption of red meat as ‘probably carcinogenic to humans’. In making this evaluation, the Working Group took into consideration all the relevant data, including the substantial epidemiological data showing a positive association between consumption of red meat and colorectal cancer and the strong mechanistic evidence. Consumption of red meat was also positively associated with pancreatic and with prostate cancer.”
Consumption of red meat varies throughout the world. In countries like the United States, almost everyone eats meat, while in some nations only 5 percent of the people do. High consumption of red meat is more than 200 grams a day, or 7 ounces, said the IARC report, which said there was less information available on processed meat. Americans are estimated by the USDA to consume nearly 5 ounces of red meat a day and roughly the same amount of poultry.
“Independent experts were cautious about the IARC’s claim,” said the Financial Times. It quoted Professor Ian Johnson, emeritus fellow at the UK’s Institute of Food Research, as saying, “Although there is epidemiological evidence for a statistically significant association between processed meat consumption and bowel cancer, it is important to emphasise that the size of the effect is relatively small, and the mechanism is poorly defined.” Johnson told the FT it would be “very inappropriate” to compare the risk from bacon and sausages with the dangers of tobacco smoke.
In its work, IARC assembles panels of expert scientists who “review the published studies and evaluate the weight of the evidence that an agent can increase the risk of cancer …. Since 1971, more than 900 agents have been evaluated, of which 400 have been identified as carcinogenic, probably carcinogenic or possibly carcinogenic to humans.” The assessments of chemicals, mixtures, occupational exposures, physical agents, biological agents and lifestyle factors are available to national health agencies in deciding their actions to prevent exposure to potential carcinogens.
IARC classifies carcinogens in five categories that indicate the weight of evidence that an agent is capable of causing cancer, which it calls the hazard. IARC does not measure the likelihood, which it calls risk, that cancer will occur as a result of exposure to the agent. “The distinction between hazard and risk is important,” says IARC. The risk associated with agents given the same classification “may be very different, depending on factors such as the type and extent of exposure and the strength of the effect of the agent.”
On March 20, IARC listed glyphosate, the most widely used weedkiller in the world, as probably carcinogenic to humans. Exposure of the general population to the chemical “is generally low,” it said. Use of glyphosate increased sharply with adoption of genetically engineered crops such as corn, soybeans, cotton and sugar beets. Monsanto Co., which uses glyphosate as the main ingredient in its Roundup herbicide, says the chemical is safe and is trying to convince other scientific agencies to accept its view.