Red Meat and Processed Meat and the Risk of Cancer

BY REBECCA SLUTSKY

It’s a tough time for lovers of hot dogs, bacon and beef jerky. After twenty years of research, the World Health Organization’s cancer research group recently announced that there is significant evidence that processed meat is a carcinogen that can cause colorectal cancer in humans.¹ In addition, the research concluded that there was strong, but still limited, evidence of a connection between eating unprocessed red meat and colorectal cancer. The group’s data also showed a link between eating processed meat and an increased risk of developing stomach cancer, as well as, according to the journal Lancet Oncology, an association between red meat and cancers of the pancreas and prostate.² The suspected link between red meat and cancer has been mounting for years, but this concrete evidence is now leaving many consumers wondering what foods are safe to eat and whether we all need to become vegetarians or vegans.

What is the World Health Organization (WHO) and why are they involved with this research? WHO is an agency of the United Nations, headquartered in Geneva, Switzerland. Its mission is to improve global public health by preventing diseases through research and dissemination of information to governments around the world. According to WHO, red meat and processed meat need to be classified separately in terms of cancer risk. Red meat refers to all muscle meat from mammals, including beef, veal, pork, and lamb. It also includes mutton, horse, and goat, which are consumed throughout the world.³ Processed meat refers to meat that is not sold fresh, meaning meat that has been transformed through salting, smoking, curing, fermentation, or adding chemical preservatives to enhance flavor or improve preservation.⁴ These may include cold cuts, ham, pepperoni, corned beef, sausages and canned meat. Hamburgers and minced meat are only considered processed meat if they have been preserved with salt or chemical additives.⁵

The WHO committee that issued the new report on October 26, 2015 was the International Agency for Research on Cancer (IARC). This group focuses their research on environmental and lifestyle factors that may contribute to cancer. For the past 45 years, the group has evaluated more than 900 different factors as part of its “Monographs” program, assigning each factor to one of five different classification groups based on the probability of it causing cancer. About 120 of these factors have been placed in the agency’s Group 1 category, meaning the factor is carcinogenic to humans. The other groups range in classification from ‘probably carcinogenic’ (Group 2), ‘possibly carcinogenic’ (Group 3), ‘not classifiable’ (Group 4) and ‘probably not carcinogenic’ (Group 5).³ These rankings demonstrate the IARC’s confidence that a factor causes cancer, but not how hazardous that factor is in causing cancer. Further, the IARC does not make specific health recommendations. Instead, the IARC Monographs are used to guide policies both nationally and internationally in order to minimize cancer risks. For example, governments may choose to include the cancer hazards of a targeted factor in their dietary guidelines.¹

The IARC committee, which consisted of 22 public health and cancer agencies from 10 countries, spent two years reviewing and evaluating 800 studies conducted over the past 20 years that investigated associations of more than 12 types of cancer with the consumption of processed or unprocessed red meat in many countries with diverse diets. Some of the studies provided data on both types of meat. More than 700 epidemiological studies provided data on red meat and over 400 epidemiological studies provided data on processed meat.⁶ After thoroughly evaluating these studies, the IARC classified the consumption of red meat as probably carcinogenic to humans (Group 2).⁷ This link was observed mainly for colorectal cancer, but associations were also seen for pancreatic and prostate cancer. Even more alarmingly, processed meat was classified in Group 1 as carcinogenic to humans. This classification was based on sufficient evidence in humans that eating processed meat is linked to colorectal cancer.⁸ An association with stomach cancer was also seen but the evidence was not conclusive. While other factors placed in Group 1 include alcohol, asbestos and tobacco, they do not all share the same hazardous level of risk. The cancer risk of asbestos and tobacco is much greater than the risk associated with eating processed meat.¹ However all factors placed in Group 1 are concluded to be carcinogenic to humans. Therefore, the risk of eating processed meat is small but real. This reality is important for worldwide public health because processed and unprocessed meat consumption is increasing not only in underprivileged communities in the United States, who tend to buy “cheaper” meats, but also in low- and middle-income countries around the world.

The WHO report has identified some of the ways red meat and processed meat may increase cancer risk, although research continues in order to fully understand the specific epidemiologic connection. The main culprits appear to be certain chemicals found in the meat itself. Red meat contains the chemical haem, which is part of the red pigment in the blood of the meat. Haem is broken down in our intestines to create a series of chemicals called N-nitroso compounds.⁴ These compounds damage the lining of the colon, so that the cells in the lining have to replicate more in order to heal. This increased cell replication can increase the risk of errors developing in the cells’ DNA that can possibly lead to cancerous cells forming in the lining of the colon.⁷ Further, in order to process meat, nitrites are used as preservatives to prevent bacterial growth and as coloring agents. However, nitrites can form the N-nitroso compounds, which are cancer-causing agents.⁵ Cooking meat at high temperatures, such as grilling, frying or broiling, can form two cancer promoting chemicals, heterocyclic amines (HCAs) and polycyclic aromatic hydrocarbons (PAHs). PAHs are specifically found in the char on the outside of the meat.¹

Just how big is your risk of cancer if you eat processed meats (independent from other environmental and lifestyle habits)? According to an independent academic research group called The Global Burden of Disease Project, about 34,000 cancer deaths per year worldwide are caused by diets high in processed meat. Further, the group estimates that diets high in red meat could cause at least 50,000 cancer deaths per year around the world.¹ To give some perspective, there are about 1 million cancer deaths worldwide each year from tobacco smoking and 600,000 people worldwide die each year from alcohol consumption.¹ The WHO data indicates that a person who eats slightly less than 2 ounces of processed meat a day (a small hot dog or 2 slices of cold cut) is 18% more likely to develop colorectal cancer than another person who eats no processed meat.⁷ “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 Dr. Kurt Straif, Head of the IARC Monographs Program. Furthermore, “in view of the large number of people who consume processed meat, the global impact on cancer incidence is of public health importance.”⁶

There have been major debates over the WHO findings on the cancer link, including significant resistance from the meat industry on one hand, and from environmental groups on the other, who are calling for warning labels on processed meat. The National Cattlemen’s Beef Association (NCBA) believes the evidence does not support the link between meat and cancer. The NCBA asserts that it is not realistic to isolate a single food as a cancer-causing agent from an entire dietary pattern, especially as it is complicated by lifestyle and environmental factors. The NCBA believes the studies on red meat consumption and cancer are weak and, therefore, it is wrong to conclude that red meat is an independent cause of cancer. It is also critical of the IARC review process and accuses the group of secrecy, selective inclusion or exclusion of studies and an overly general interpretation of study results.⁹ Therefore, the meat industry continues to assert that its products are safe to eat as part of a balanced diet. On the other end of the spectrum, states like California, which has taken the lead in consumer-oriented initiatives, are evaluating the WHO results to determine whether to add red meat and processed meat to a cancer-alert list. The inclusion of red meat and processed meat on the list could reduce consumer demand and hurt major producers and processing companies. It could also encourage consumers diagnosed with colorectal cancer to sue the meat companies costing them billions of dollars and potentially bankrupting them.¹⁰ Nevertheless, the environmental group, Center for Biological Diversity, believes that since WHO has put processed meat in the same category as cigarettes in terms of certain cancer risk, states need to come forward with public health warnings in the form of labels on meat packaging, signs, or menu notation where the meat is sold.¹¹ Needless to say, the debate on both sides will continue in America and worldwide.

Can a healthy diet still include meat and processed meat? Although the WHO report does not make dietary recommendations, the American Cancer Society Guidelines on Nutritional and Physical Activity and Cancer Prevention currently advises people “to limit how much processed meat and red meat they eat.”³ Guidance from the American Institute for Cancer Research (AICR) includes specific amounts of meat in its dietary recommendations. They recommend that people avoid eating processed meat, or reserve eating it to only a few special occasions per year.⁵ For red meat, the AICR recommendations call for eating no more than 18 ounces of cooked red meat per week. This equals six card-deck size portions, or 3-ounce servings, of red meat weekly.⁴ It is important to remember that eating red meat in moderation is fine as it can be a good source of nutrients including protein, iron and zinc.⁸ In developing countries, governments and international regulatory agencies need to conduct risk assessments in order to balance the risks and benefits to its people. But trying to eat smaller portions of red meat by adding more beans, fruits, vegetables and fish in your diet are all healthy ways to lower risk of cancer. In fact, plant based foods contain polyphenols, which are determined to be dietary antioxidants that offer protection against the development of cancers.¹² So remember to eat your vegetables. Tofu is still optional!

Rebecca Slutsky is a junior in Silliman College majoring in Molecular, Cellular & Developmental Biology. She can be contacted at rebecca.slutsky@yale.edu.

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References:

1. “Q&A on the Carcinogenicity of the Consumption of Red Meat and Processed Meat.” World Health Organization. World Health Organization, Oct. 2015. Web. 09 Feb. 2016.
2. “Red and Processed Meat and Cancer Prevention | World Cancer Research Fund UK.” World Cancer Research Fund, n.d. Web. 09 Feb. 2016.
3. O’connor, Anahad. “Meat Is Linked to Higher Cancer Risk, W.H.O. Report Finds.” The New York Times. The New York Times, 26 Oct. 2015. Web. 09 Feb. 2016.
4. Dunlop, Casey. “Processed Meat and Cancer – What You Need To Know.” Cancer Research UK. HomeAbout Us Cancer NewsScience Blog, 26 Oct. 2015. Web. 09 Feb. 2016.
5. “Our Work, Our Impact, Our Solutions.” The Facts About Red Meat & Processed Meat. American Institute for Cancer Research, n.d. Web. 09 Feb. 2016.
6. “IARC Monographs on the Evaluation of Carcinogenic Risks to Humans.” IARC Monographs on the Evaluation of Carcinogenic Risks to Humans. World Health Organization, 26 Oct. 2015. Web. 09 Feb. 2016
7. Santarelli, RL, F. Pierre, and DE Corpet. “Processed Meat and Colorectal Cancer: A Review or Epidemiological and Experimental Evidence.” Pubmed, 2008. Web.
8. “World Cancer Research Fund Response to the Latest Evidence on Meat & Cancer Risk.” World Cancer Research Fund, n.d. Web.
9. “News Releases – Beef USA.” Science Does Not Support International Agency Opinion on Red Meat and Cancer –. National Cattlemen’s Beef Association, 26 Oct. 2015. Web. 11 Feb. 2016. <https://www.beefusa.org/newsreleases1.aspx?newsid=5418&gt;.
10. Polansek, Tom, and PJ Huffstutter. “California Considers Adding Meat to Cancer-alert List.” Reuters. Thomson Reuters, 28 Oct. 2015. Web. 09 Feb. 2016.
11. O’Connor, Lydia. “Bacon May Soon Come With a Warning Label in California.” Huffpost Politics. Huffington Post, 26 Oct. 2015. Web.
12. Pandey, Kanti Bhooshan, and Syed Ibrahim Rizvi. “Plant Polyphenols as Dietary Antioxidants in Human Health and Disease.” Oxidative Medicine and Cellular Longevity. Landes Bioscience, n.d. Web. 22 Feb. 2016. <http://www.ncbi.nim.nih.gov/pmc/articles/PMC2835915/&gt;