Processed Meat Increases Risk for Colon Cancer, Says IARC
Processed Meat Increases Risk for Colon Cancer, Says IARC
Roxanne Nelson, RN, BSN 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. AbstractEating 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
Red, Processed Meats Tied to Increased Risk for CRC Death
Advising men and women with colorectal cancer (CRC) to eat 4 or fewer servings of red and processed meat a week might be good clinical advice to improve their disease-specific survival, according to a new observational study.
Investigators from the American Cancer Society (ACS) found that survivors with consistently high intakes (median of about 4 servings/week or higher) before and after diagnosis had a 79% higher risk for CRC-specific mortality (relative risk, 1.79) than those with intakes consistently below the median.
The increased risk in the high consumers was statistically significant, according to the authors, led by Marjorie McCullough, ScD, from the epidemiology research program at the ACS.
Their study of CRC survivors and meat consumption was published online July 1 in the Journal of Clinical Oncology.
However, such dietary advice to CRC survivors is “speculative” and needs to be clarified with further cohorts, writes Jeffrey Meyerhardt, MD, in an accompanying editorial. He is from the Dana-Farber Cancer Institute in Boston.
Both the authors and Dr. Meyerhardt agree that there is strong evidence that eating red and processed meat increases the risk of developing CRC.
“Studies of red meat and processed meat have been a rare example of fairly consistent results showing an association between increased intake and risk of developing colorectal cancer,” writes Dr. Meyerhardt.
Public health guidelines recommend limiting the consumption of these types of meats for cancer prevention, say Dr. McCullough and colleagues.
However, both the authors and editorialist point out that there is scant evidence on how meat intake influences CRC-related mortality after diagnosis.
The authors undertook their study to address that issue.
Dr. McCullough and colleagues reviewed data from the Cancer Prevention Study II Nutrition Cohort and found 2315 men and women who were diagnosed with colon or rectal cancer between 1992 and 2009.
Of the 966 patients who died during the study period, 413 died from CRC.
The authors looked at meat intake before and after the diagnosis of CRC.
Notably, on multivariable analysis, overall meat intake after diagnosis was not associated with death from CRC.
This is a “curious finding,” says Dr. Meyerhardt. But the authors argue that meat consumption has to be looked at both before and after diagnosis. They explain that adverse effects from CRC surgery and adjuvant treatment can influence subsequent diet, and that the cohort database did not include such appetite-related information. In other words, after treatment, some patients won’t feel like eating much meat. Thus, the study data from this period of time (after diagnosis) are not strong.
Therefore, the authors focused on “long-term” meat consumption, which could be “a more relevant measure and may be better represented by prediagnostic diet than by postdiagnostic diet.”
Over this stretch of time, it looks like eating a lot of meat increased the risk of dying from CRC. “Men and women who consistently ate the most red and processed meat before and after diagnosis had a statistically significant higher risk of death as a result of CRC, compared with those who consistently ate the least red and processed meat,” the authors note.
The authors have disclosed no relevant financial relationships.
Diets Heavy in Meat Boost Risk for Certain Cancers
A new multicountry study provides more evidence that certain dietary and lifestyle factors can increase the risk of developing cancer.
Results from the study, published in the January issue of Nutrients, show that smoking and 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 contrast, alcohol consumption was found to be significantly correlated with only colorectal cancer.
Added sweeteners were also associated with an increased incidence of brain cancer in women, and in corpus uteri, pancreatic, and prostate cancers. Cereals were associated with a decreased incidence of kidney and prostate cancer.
“My study reiterates that animal products are an important risk factor for many types of cancer,” said study author William B. Grant, PhD, from the Sunlight, Nutrition, and Health Research Center in San Francisco.
The data also show that there is a 15- to 30-year lag between diet and cancer incidence. Eating animal products is as important as smoking for increasing the incidence of all cancer types (apart from lung cancer), Dr. Grant noted.
Interestingly, animal fat is an important risk factor for lung cancer. “This helps explain why lung cancer rates have increased dramatically in Japan, even though smoking rates have not,” he told Medscape Medical News. “As they made the nutrition transition from the traditional Japanese diet to the Western diet, rates of cancers common in Western developed countries, such as breast, colorectal, and prostate, increased with about a 20-year lag.”
In addition, Alzheimer’s disease rates for those older than 65 years increased in Japan from 1% in 1985 to 7% in 2008.
According to the World Health Organization (WHO), approximately 30% of cancer mortality is due to the 5 leading behavioral and dietary risks: high body mass index, low fruit and vegetable intake, lack of physical activity, tobacco use, and alcohol use. Tobacco use is the most important risk factor, accounting for 22% of global cancer deaths and 71% of global lung cancer deaths.
In recent years, several organizations, including the American Institute for Cancer Research (AICR), the American Cancer Society (ACS), 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 recommends limiting the intake of red and processed meat, eating mostly foods of plant origin, and limiting the consumption of energy-dense foods, which includes sugary drinks.
Dr. Grant’s work is an ecological study that examines the association between incidence rates for 21 types of cancer in both men and women from 157 countries (87 with high-quality data) and various risk-modifying factors.
The rates are from 2008 and were obtained from the International Agency for Research on Cancer of the WHO, and dietary supply data came from the Food and Agriculture Organization. Data going back to 1980 were included because there is typically a lag time of up to 20 years between dietary changes and peak cancer rates.
The animal products index in this study included meat, milk, fish, and eggs. Dr. Grant also used lung cancer incidence rates as an index for the effects of smoking and air pollution, because this integrates the effect of all factors contributing to lung cancer and other cancers linked to lifetime smoking.
Latitude, Vitamin D, and Cancer
Dr. Grant explained that he looked at latitude as a an index of solar UVB doses, which is an important source of vitamin D. In fact, he found that higher latitudes (where there is less UVB, and consequently less vitamin D absorption) were associated with higher rates of cancer.
In the 87 countries for which high-quality data were available, there was an increase in the incidence of bladder, colorectal, kidney, and lung cancers, and in melanoma and Hodgkin’s lymphoma. When all 157 countries studied were taken into account, an increased incidence of brain and breast cancer was seen at higher latitudes.
“These results add support to other studies that have found that UVB and vitamin D reduce the risk of many types of cancer,” he said.
For melanoma, however, the result are primarily related to changes in skin pigmentation with latitude, Dr. Grant explained. “There is very little melanoma within 30 degrees of the equator for people living in their ancestral homelands, since they have dark enough skin to protect against melanoma.”
Conversely, Australia and New Zealand have the highest rates of melanoma and are populated primarily by individuals with Northern European ancestry.
Marji McCullough, ScD, RD, strategic director of nutritional epidemiology at the ACS, noted that this study is consistent with other studies that show that healthy lifestyle behaviors can modify the risk for many types of cancer.
However, she explained, the problem with ecological studies such as this one is that they are hypothesis-generating, and estimates are made across large groups. In this case, diet is measured over populations rather than individuals. Thus, there can be issues with measuring the data and accounting for confounders.
“The ACS recommends limiting red and processed meats, and instead choosing poultry, fish, nuts, and legumes as alternative sources of protein,” Dr. McCullough told Medscape Medical News. “But in this study, all animal products are grouped together, so we can’t be sure what it means or which ones are being consumed.”
“It would be valuable to have a breakdown of the types of animal products so we know what people were actually eating,” she said, “and to have more detail.”
Dr. Grant acknowledged that he was unable to separate the types of animal products, so he could not show a relation between any specific item and cancer incidence. “The limitation of my study is that different countries have different amounts of animal products from the various types of animal products,” he said. “However, all animal products are high in fat and/or protein, and both increase the production of insulin-like growth factor 1, which encourages bodies — and tumors — to grow.”
Dr. Grant has disclosed no relevant financial relationships.
Nutrients. 2014;6:163-189. Abstract
Strong Evidence Links Meat to Higher Risk for Colon Cancer
new report has confirmed that red and processed meat increases the risk for colorectal cancer, and the evidence that foods containing fiber offer protection against the disease has become stronger.May 30, 2011 — A
The report, released as part of the World Cancer Research Fund/American Institute for Cancer Research (WCRF/AICR) groundbreaking Continuous Update Project (CUP), examined the relation between the risk for colorectal cancer and diet, physical activity, and weight.
According to the findings, it is 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. That would prevent more than 64,000 cases in the United States every year.
Update of Earlier Report
WCRF/AICR-funded scientists at Imperial College London, United Kingdom, conducted a systematic review of the literature, which added 263 papers on colorectal cancer to the 749 that were analyzed as part of the 2007 report. An independent expert panel then reviewed the results and made judgments.
The findings of the WCRF/AICR’s 2007 report, Food, Nutrition, Physical Activity, and the Prevention of Cancer: A Global Perspective, have been updated accordingly.
“Our review has found strong evidence that many cases of bowel cancer are not inevitable, and that people can significantly reduce their risk by making changes to their diet and lifestyle,” said Alan Jackson, MD, chair of the WCRF/AICR CUP expert panel, in a statement.
He added that there has been a lot of debate during the past few years about the strength of evidence suggesting that red and processed meat increases the risk for cancer. “We hope our review can give clarity to people who are still confused about the strength of the evidence,” Dr. Jackson explained.
“Because our judgments are based on more evidence than ever before, it means the public can be confident that this represents the best advice available on preventing bowel cancer,” he added. “On meat, the clear message that comes out of our report is that red and processed meat increase risk of bowel cancer and that people who want to reduce their risk should consider cutting down the amount they eat.”
Barriers to Improving Health
Colon cancer is one of the most preventable cancers there is, and this is a ‘teaching moment’ for physicians.
Alice Bender, MS, RD, a nutritionist at AICR, acknowledges that simply putting out a message doesn’t mean that people will automatically change their eating and lifestyle habits. “There are a lot of barriers to improving health,” she said in an interview. “But colon cancer is one of the most preventable cancers there is, and this is a ‘teaching moment’ for physicians.”
Physicians can emphasize the preventability aspect of making lifestyle changes along with other initiatives, such as screening, she explained.
Ms. Bender pointed out that none of these diseases exist in isolation. “If something impacts the risk in one disease, then it generally will impact another,” she said. “In this case, the recommendations can help lower the risk of other chronic diseases, such as diabetes.”
Ms. Bender also acknowledges that many physicians are busy and have limited time to counsel patients about diet and lifestyle. “In that case, referrals can be made to other professionals, such as registered dieticians,” she said. “Dieticians will have more time than physicians to really discuss these issues and help patients make changes.”
Support From Other Guidelines
Both the US Department of Agriculture (USDA) and the American Cancer Society (ACS) have issued guidelines that echo many of the recommendations of the WCRF/AICR report. The USDA guidelines, which were released earlier this year and are geared toward reversing the rate of overweight and obese people, place a more pronounced emphasis on reducing caloric intake and increasing physical activity, and recommend increasing the intake of fruit, vegetables, whole grains, and fiber.
As previously reported by Medscape Medical News, the USDA guidelines overlap much of the advice from the WCRF/AICR and ACS, but there is one notable difference between them: the USDA does not recommend limiting red and processed meat, whereas the ACS and WCRF/AICR do.
The ACS recommendation for reducing the intake of red and processed meat was made on the basis of a wealth of studies showing increased colorectal cancer risk, Marji McCullough, ScD, RD, strategic director of nutritional epidemiology at the ACS, previously told Medscape Medical News.
New Data Support 2007 Recommendations
For red and processed meat, the findings from 10 new studies were added to the 14 studies that were evaluated in the 2007 report. From these 24 studies, the panel confirmed that there is convincing evidence that both red and processed meat can increase the risk for colorectal cancer.
The WCRF/AICR recommend that the consumption of red meat be limited to 500 g/week, which is roughly the equivalent of 5 or 6 medium portions of beef, lamb, or pork. They also recommend that processed meat be avoided.
According to their data, if 3.5 ounces of red meat are consumed every day (24.5 ounces per week), the risk for colorectal cancer will be 17% higher than if no red meat is consumed. If the amount of red meat consumed is doubled (7.0 ounces every day; 49 ounces per week), the risk is 34% higher. However, the evidence found that there was very little increase in risk for individuals who ate less than 18 ounces of red meat per week.
The cancer risk associated with processed meat, which includes ham, bacon, pastrami, hot dogs, and sausages, was much higher. Consuming 3.5 ounces every day (24.5 ounces per week) was associated with a risk that is 36% higher than the risk of consuming no processed meat. As with red meat, the higher the rate of consumption, the higher the risk for colorectal cancer.
There were 15 cohort studies included in the update that investigated the association between alcohol consumption and cancer. Overall, the experts found that all cohort studies showed an increased risk for colorectal and colon cancers with higher intake. This evidence is consistent with the earlier conclusions, they write, in that “ethanol from alcoholic drinks as a cause of colorectal cancer in men is convincing; and it is probably a cause in women.”
The updated report reaffirms AICR’s recommendation that individuals consume a plant-based diet that includes foods containing fiber, such as whole grains, fruits, vegetables, and beans, they write.
Elisa Bandera, MD, PhD, who is a member of the CUP expert panel, noted that many people are confused about cancer prevention because “it can seem like a new study is published every week that suggests something either causes or prevents cancer.”
“But the CUP takes the latest scientific findings and adds them to the existing body of evidence in a systematic way that ensures our advice takes the latest research into account,” Dr. Bandera, who is from the Cancer Institute of New Jersey, New Brunswick, said in a statement. “This means people can be confident that AICR’s recommendations represent the most up-to-date, evidence–based information on cancer prevention available.”