Processed Meat Increases Risk for Colon Cancer, Says IARC

Roxanne Nelson, RN, BSN

October 27, 2015

Eating processed meat, including bacon, cold cuts, sausages, and hot dogs, can increase the risk of developing colorectal cancer, according to a new report from the World Health Organization (WHO).

The International Agency for Research on Cancer (IARC), the cancer agency of the WHO, has classified consumption of processed meat as "carcinogenic to humans" (Group 1) on the basis of sufficient evidence for colorectal cancer. In addition, says the group, there was a positive association with stomach cancer.

The IARC has also classified the consumption of red meat as being "probably carcinogenic to humans" (Group 2A). The decision was based on all of the relevant data that show strong mechanistic evidence supporting a carcinogenic effect. This association was observed mainly for colorectal cancer but also for pancreatic cancer and prostate cancer.

An analysis of data from 10 studies estimated that every 50-g portion of processed meat eaten daily increases the risk for colorectal cancer by about 18%.

The IARC acknowledges that it is more difficult to estimate the cancer risk related to consuming red meat (that is not processed) because the evidence linking it to cancer is not as strong as it is for processed meats. However, if the association of red meat and colorectal cancer were proven to be causal, data from the same studies suggest that the risk for colorectal cancer could increase by 17% for every 100-g portion of red meat eaten daily.

"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," says Kurt Straif, MD, PhD, head of the IARC Monographs Programme. "In view of the large number of people who consume processed meat, the global impact on cancer incidence is of public health importance."

A summary of the evaluations was published online October 26 in the Lancet Oncology.

The consumption of meat varies greatly between countries, from less than 5% to up to 100%. For processed meat, it varies from less than 2% to 65%. The mean intake of red meat by those who consume it is about 50 to 100 g per person per day, with high consumption equalling more than 200 g per person per day, according to the report. Less information is available on the consumption of processed meat.

Previous Data Point to Risk

As previously reported by Medscape Medical News, the long-term consumption of red meat and processed meat has repeatedly been associated with a higher risk for certain cancers, especially colorectal cancer. Research has also suggested a link between the heavy consumption of red meat during premenopausal years and an increased risk for breast cancer.

Other data show that smoking and consuming diets rich in animal products have the strongest correlations with cancer incidence rates. The strongest correlation with animal products was seen in cancers of the female breast, corpus uteri, kidney, ovaries, pancreas, prostate, testicles, and thyroid, and in multiple myeloma.

In recent years, several organizations, including the American Institute for Cancer Research (AICR), the American Cancer Society, and the US Department of Agriculture, have issued dietary guidelines aimed at encouraging healthier eating habits, increasing physical activity, and curbing rising obesity rates.

Some of the most extensive data on diet/lifestyle and cancer risk have been released by the AICR, which confirmed that consumption of red meat and processed meat increases the risk for colorectal cancer. The AICR recommended limiting the intake of red meat and processed meat, eating mostly foods of plant origin, and limiting the consumption of energy-dense foods, which include sugary drinks. In their 2011 report, they estimated that about 45% of colorectal cancer cases could be prevented if people consumed more fiber-rich plant foods, consumed less meat and alcohol, became more physically active, and maintained a healthy weight.

Methods Used

The IARC convened a working group of 22 experts from 10 countries who reviewed the accumulated scientific literature. They experts considered more than 800 studies that investigated associations of more than a dozen types of cancer with the consumption of red meat or processed meat in many countries and populations with diverse diets. The most influential evidence came from large, prospective, cohort studies conducted over the past 20 years.

The largest body of epidemiologic data concerned colorectal cancer. For example, one meta-analysis of 10 cohort studies reported a statistically significant dose-response relationship, with a 17% increased risk (95% confidence interval [CI], 1.05 - 1.31) per 100 g per day of red meat and an 18% increase (95% CI, 1.10 - 1.28) per 50 g per day of processed meat (PLoS One. 2011;6:e20456).

Data were also available for more than 15 other types of cancer. The most positive associations were observed in cohort studies and population-based case-control studies between consumption of red meat and cancers of the pancreas and the prostate (primarily advanced prostate cancer) and between consumption of processed meat and cancer of the stomach.

Accolades and Thumbs Down

Susan Gapstur, MPH, PhD, vice president of epidemiology, American Cancer Society, commented that "this is an important step in helping individuals make healthier dietary choices to reduce their risk of colorectal cancer in particular."

"In general, the IARC conclusion is consistent with the World Cancer Research Fund/AICR Continuous Update Project, which found the evidence convincing that diets high in red meat and processed meat are associated with increased risk of colorectal cancer," she said in a statement.

Classifying processed meat as carcinogenic and red meat as probably carcinogenic to humans is not unexpected, she pointed out. "Indeed, based on earlier scientific studies, including findings from the American Cancer Society's Cancer Prevention Study II, the American Cancer Society has recommended limiting consumption of red and processed meat specifically since 2002."

Dr Gapstur added that the IARC report is also in line with the US 2015 Dietary Guidelines for Americans Advisory Committee, which recommends a healthful dietary pattern that is lower in red meat and processed meat.

Not surprisingly, the release of the IARC report was not well received among the meat industry, which immediately pushed back against the findings.

In a release, the North American Meat Institute (NAMI) said that classifying red meat and processed meat as cancer "hazards" defies "both common sense and numerous studies showing no correlation between meat and cancer and many more studies showing the many health benefits of balanced diets that include meat."

"It was clear sitting in the IARC meeting that many of the panelists were aiming for a specific result despite old, weak, inconsistent, self-reported intake data," said Betsy Booren, PhD, NAMI vice president of scientific affairs. "They tortured the data to ensure a specific outcome.

"Red and processed meat are among 940 agents reviewed by IARC and found to pose some level of theoretical 'hazard.' Only one substance, a chemical in yoga pants, has been declared by IARC not to cause cancer," said Dr Booren.

The National Cattlemen's Beef Association (NCBA) noted that "after 7 days of deliberation in Lyon, France, IARC was unable to reach a consensus agreement from a group of 22 experts in the field of cancer research, something that IARC has proudly highlighted they strive for and typically achieve. In this case, they had to settle for 'majority' agreement."

"Cancer is a complex disease that even the best and brightest minds don't fully understand," said Shalene McNeill, PhD, RD, executive director of human nutrition research at the NCBA, in their press release. "Billions of dollars have been spent on studies all over the world, and no single food has ever been proven to cause or cure cancer.

"The opinion by the IARC committee to list red meat as a probable carcinogen does not change that fact," said Dr McNeill. "The available scientific evidence simply does not support a causal relationship between red or processed meat and any type of cancer."

Lancet Oncol. Published online October 26, 2015. Abstract

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