In October 2015, the World Health Organization (WHO) released a report by the International Agency for Research on Cancer (IARC), which for the first time listed processed meat as “carcinogenic to humans” and red meat as “probably carcinogenic to humans.” This report specifically identified both types of meat as potential causes of colorectal cancer. This fact sheet is intended to help readers understand the research behind this report, as well as the report’s implications for health and well-being.
What are processed meats and red meat?
Red meat is muscle meat that comes from mammals. Examples of red meat include hamburgers, steak, ham, sausage and pork. You may remember the popular slogan, “pork, the other white meat,” and find its inclusion in the current list of red meats confusing. The slogan was created to showcase pork’s lowered fat content over the years, which has become similar to some chicken’s low-fat content. Although advertisements have identified pork as a “white meat,” it still comes from mammal muscle and is recognized as a red meat in the current research.
The traditional alternatives to red meat are “white meat,” fish and shellfish. White meat in the current research includes all poultry, such as chicken, turkey, duck and goose, among others. Both red meat and white meat can be either processed or unprocessed.
Processed meat is any meat which has undergone processing. There are many forms of processing, but the most common include smoking, curing, salting and chemically preserving. Meats are usually processed to safely lengthen shelf-life, improve taste, or change a meat’s consistency. Common processed meats include bacon, sausage patties, chicken nuggets, jerkies, lunch meats/cold-cut meats, pepperoni, hot dogs and bratwurst.
In the United States, approximately 58 percent of the meat adults actually consume is red and 22 percent is processed.
What is colorectal cancer?
Colorectal cancer is any cancer which appears in the colon or rectum. Both the colon and rectum are located in the large intestine. Colorectal cancer includes both colon cancer and rectal cancer.
While the rate of colorectal cancer has been steadily decreasing over the past twenty years, it still remains the fourth most common type of cancer (behind breast cancer, lung cancer and prostate cancer). In 2014, there were over 1 million people living in the United States with colon or rectal cancer. It is estimated there were over 134,000 new cases of colon and rectal cancer in 2016, making up about 8 percent of all new cancer cases in the United States.
What is the IARC and what does it do?
The IARC is an independent agency which researches and monitors cancer-causing substances in our environment. The IARC provides research into substances’ risk of causing cancer, from food to chemicals to natural substances. This agency publishes a journal called The IARC Monographs. The Monographs publish reviews of studies that research the links between cancer and various substances, foods and other factors. In other words, it seeks to determine if there is enough scientific evidence across research studies to call for a substance to be listed as carcinogenic.
Based on these extensive reviews, the IARC divides researched factors/substances into groups that identify them as…
“Group 1: Carcinogenic to humans,
Group 2A: Probably carcinogenic to humans,
Group 2B: Possibly carcinogenic to humans,
Group 3: Not classifiable as to its carcinogenicity to humans,” or
“Group 4: Probably not carcinogenic to humans. (IARC, 2016).”
Over 500 substances including food fall into Group 3, meaning they cannot be classified as causing or not causing cancer. Only one researched substance, Caprolactum, falls within Group 4 and is known to not cause cancer. On the other hand, 289 substances are believed to probably cause cancer (Group 2A), 80 substances are believed to possibly cause cancer (Group 2B), and 118 substances are known to cause cancer based on the available scientific evidence (Group 1).
What did the IARC report find?
The IARC reviewed over 800 studies from around the world that analyzed the risk of cancer from both red and processed meat. The important general findings of this review were:
- Roughly half of the reviewed studies examining human cancer and red meat consumption showed an association between red-meat and colorectal cancer.
- The majority of studies examining human cancer and processed meat consumption demonstrated a positive association between processed meat consumption and colorectal cancer.
- From the data across studies, the IARC determined that for every 50 grams of processed meat eaten daily, the risk of colorectal cancer increased by 18 percent.
Fifty grams of processed meat is equivalent to just 1.8 ounces of meat, equal to the following amounts of processed meats:
- A little over two slices of turkey-breast lunch meat.
- A little under three average chicken nuggets.
- A little over half of an average bratwurst link.
Due to these findings, The IARC classified red meat as probably causing cancer (Group 2A) and processed meat as definitely causing cancer (Group 1). Red meat was identified as probably causing colorectal cancer because roughly half the studies showed an association between cancer and red meat, but the other half of the studies did not show this association. On the other hand, the link between colorectal cancer and processed meat was regularly shown across most of the 800 studies.
Thus, processed meat was placed in the same cancer risk group as smoking—a known cause of cancer. But red meat was placed in a group representing a likely cause of cancer.
Why would processed meat and red meat cause cancer?
Because researchers cannot ethically control what individuals eat, it is difficult to determine the exact causes for red and processed meats’ link with colorectal cancer. Much of the current evidence comes from studies observing groups of people and comparing reported meat consumption habits from those who develop colorectal cancer to those who don’t develop colorectal cancer. These studies are useful in telling us that an association exists between meat and colorectal cancer, but the studies do not provide an understanding of what causes colorectal cancer.
Studies involving mice have provided possible causal explanations. These possible explanations include five ideas:
- High fat consumption promotes the secretion of bile acids into the small intestine which may play a part in promoting tumors in the colon and rectum. Because many processed and red meats are high in fat, this could partially explain their link to cancer. Of course, all processed and red meats are not high in fat, and many other non-meat foods are high in fat, but are not associated with increased risk of cancer. Thus, high fat in some red and processed meats cannot provide a full explanation of their association with colorectal cancer.
- Cooking meat at high temperatures causes the formation of Heterocyclic Amines (HCAs) and Polycyclic Aromatic Hydrocarbons (PAHs), substances that are known to cause cancer. Because most processed and red meats are exposed to high cooking temperatures, this may explain their link with colorectal cancer. However, other unprocessed and white meats are also exposed to the same high cooking temperatures. Thus, this also cannot solely explain the link between colorectal cancer and processed and red meat.
- Heme iron (naturally found in animal muscles and blood cells) initiates the natural formation of cancer-causing compounds in the colon and rectum known as N-nitroso compounds (NOCs). Because heme iron has a lower presence in white meat than in red meat, this may help explain the possible association between red meat and cancer.
- Nitrites, nitrates and their associated compounds are preservatives that help to maintain the shelf-life and food safety of processed meats. These preservatives are believed to contribute to the formation of additional NOCs/carcinogenic compounds in the colon. Because these nitrites are found exclusively in processed meats, this may help explain the known association between processed meats and cancer.
- When both heme iron and nitrite compounds are present in a processed, red meat, they interact, leading to an increased development of those natural carcinogenic compounds—the NOCs—in the digestive system. These “extra” carcinogenic compounds are formed in addition to those NOCs which would already be formed due to consumption of regular red meat. This again, could help explain the strong association between processed meat and colorectal cancer. But it could also help explain why red meat has a less clear association with colorectal cancer.
It is not known which (or if any) of the above theories truly explains the association between processed and red meat and cancer, but research is currently focused on exploring these possible explanations further. In addition, new theories are being developed that could help explain the unique association between cancer and processed and red meat in the future.
Are red and processed meats the only risks for developing colorectal cancer?
The simple answer to this is “no.” There are many believed links to colon and rectal cancer. Some of these links include:
- Experience of inflammatory bowel diseases (for example Crohn’s disease).
- A family history of colon or rectal cancer.
- Inactive lifestyles.
- Diets low in fruits and vegetables.
- Diets low in fiber.
- Diets high in excess fat.
- Alcohol consumption.
Because there are so many factors associated with colorectal cancer, removing processed and red meat from the diet does not necessarily protect from developing colon or rectal cancer: Reducing processed and red meat intake is only one puzzle piece. The overall diet, general health choices, and physical activity are all important factors increasing or decreasing our risks for developing colorectal cancer.
Should you stop consuming processed and red meats?
You may have heard in the media that processed meat now bears the same cancer risk as smoking cigarettes. But it is important to understand that while the IARC has given processed meat the classification of a known carcinogen—the same classification cigarette smoke has—this does not mean cigarettes and processed meat bear equal health risks to consumers. The WHO estimates there are 34,000 global cancer deaths per year caused by processed meat. In contrast, 1 million global cancer deaths per year are caused by smoking.
Whether an individual chooses to remove processed and red meat from his or her diet is a personal decision that is best based on an understanding of the current research, your personal risk for colon cancer (based on family history, and the other factors listed above) and not the latest news headlines. It is also important to compare your personal meat consumption patterns to the current U.S. Department of Agriculture (USDA) Dietary Guideline’s recommendations for protein consumption when deciding if you should reduce your meat intake.
The USDA has not provided any specific recommendations for the consumption of processed or red meats. However, the USDA does have specific recommendations for the consumption of all protein foods, which includes meat. USDA Guidelines currently recommend most adult women and men consume between 5 and 6 ounces of protein foods (including meat) daily. However, the average consumption of meat, poultry and eggs in men ages 14 to 51 is well above recommended consumption levels. If you regularly consume large portions of meat, you may consider providing yourself with smaller serving sizes or fewer servings throughout the week. If you already meet the USDA recommendations for meat consumption, you may choose not to alter your meat consumption.
Because meat still provides valuable nutrients, the WHO calls for “limited intake” of processed meats to reduce risk of colorectal cancer. This call to limit processed meat doesn’t mean an individual should refrain from eating processed meat ever again. Instead, this call means individuals should only occasional enjoy processed meat and that it should not be part of regular, daily diets. If you currently regularly eat processed meat, set small goals to lower your overall intake, but don’t feel obligated to remove all processed meat from your diet.
The American Institute for Cancer Research (AICR) is the only organization that has provided specific recommendations for meat consumption: According to the AICR, 18 ounces of red meat weekly (or less) is recommended. The AICR’s recommendation for limited consumption of red meat is based on their reviews of the scientific research which shows that consumption of 18 ounces of red meat weekly has shown no link to an increased risk of colorectal cancer. Eighteen weekly ounces of red meat equals out to roughly 3 ounces of red meat six times per week (3 ounces of red meat are the size of a deck of cards).
How can you make healthier meat decisions?
How can you lower your consumption of red and processed meats? First, become aware of how much you are eating by keeping a food diary for a week. If you feel you are consuming too much red or processed meat in comparison to the USDA, WHO and AICR recommendations, try the following tips to help you eat less:
- Replace dinner-time red meats with other protein sources, such as fish, poultry, nuts and beans.
- Switch your processed lunch meat with other easy protein-filled lunches such as peanut butter and jelly, hummus and pita, leftover turkey/chicken in a sandwich, tuna salad, and bean soup.
- Eat an egg for breakfast. You can enjoy scrambled, sunny-side up, boiled, poached eggs and more.
- Serve yourself smaller portions of the red meat you enjoy. For example, instead of cooking yourself a 1/2 pound (8 ounce) hamburger, cook a hamburger slightly under a 1/4 pound that counts as one of your six weekly 3 ounce servings of red meat.
- Eat a variety of other foods. The greater the variety of food you eat, the less hungry you’ll be for red and processed meat.
- Set realistic weekly goals, also known as S.M.A.R.T. (Specific, Measurable, Attainable, Realistic and Timely) goals, for reducing processed and red meat consumption.
With these tips and an understanding of the WHO report on red and processed meats, you can make smart decisions on meat consumption which fit into your personal life.
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