Strong Evidence Links Meat to Higher Risk for Colon Cancer

Roxanne Nelson

May 30, 2011 — A 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.

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."