Study links meat consumption to colon cancer

A major American Cancer Society study finds people who reported the highest consumption of red and processed meat had a significantly higher risk of colorectal cancer than those who reported the least consumption. The study of nearly 150,000 Americans, the largest and most comprehensive to date, adds substantially to previous evidence linking highest consumption of red and processed meat to intestinal cancer. It is published in the Jan. 12, 2005 issue of the Journal of the American Medical Association (JAMA).

For red meat, prolonged high consumption was described as at least three ounces daily for men and two ounces daily for women over a period of 10 years. For processed meat, it meant at least one ounce per day five to six days per week for men and two to three days per week for women. Three ounces is approximately equal to the amount in one large fast-food hamburger. A piece of bologna weighs one ounce; two slices of cooked bacon weigh a little more than one-half an ounce.

“More than two dozen studies have already examined the relationship between consumption of red or processed meat and increased risk of colorectal cancer, with most showing greater risk in people with higher consumption,” said Michael J. Thun, MD, the Society’s chief of epidemiology and a co-author of the study. “Those studies along with this new one make it clear there is credible evidence that high meat consumption increases the risk of colon cancer.”

Colon cancer is the third most common cause of cancer and cancer death in both men and women, with an estimated 146,940 new cases and 56,730 deaths (or about one in ten cancer deaths) in 2004. When detected early, the five-year survival rate is 90 percent. However, only 38 percent of colorectal cancers are caught at this stage, primarily because Americans are not getting screened. (See the American Cancer Society recommendations on early detection below.)

For the study, 148,610 adults aged 50 to 74 years residing in 21 states provided information on meat consumption in 1982 and again in 1992/1993 while enrolled in the Society’s Cancer Prevention Study II (CPS II) Nutrition Cohort. Men and women reported a wide range in consumption of red and processed meats, with a 10-fold difference in between the lowest and highest quintiles of red meat consumption in men and a 17-fold difference in women. Median intake of red and processed meat was greater among men. For red meat, men averaged 427 grams per week (2.1 oz /day) compared to 274 grams per week (1.4 oz/day) for women. For processed meat, the amounts were 95 grams per week and 43 grams per week, respectively.

The study found those who ate the most red meat in both questionnaires, 10 years apart, were 30 percent more likely to develop distal colon cancer than those who ate little or no red meat (RR, 1.29). Those who ate the most processed meat were 50 percent more likely to develop distal colon cancer (RR, 1.50). The colorectal cancer risk posed by prolonged consumption of red and processed meats is similar or somewhat smaller than the risks associated with other lifestyle factors, such as physical inactivity and obesity, for which relative risks are generally estimated to be 1.5 to 2.0.

The study did not directly examine mechanisms at the root of the association. Other studies have postulated that iron in red meat, carcinogens produced by cooking at high temperatures, fat in meat and/or salt or nitrates/nitrites in processed meat could be responsible for the increased cancer risk.

The study also found long-term consumption of poultry and fish was inversely associated with the risk of both proximal and distal colon cancer, although the association was only marginally significant.

“The American Cancer Society’s guidelines on nutrition and physical activity currently recommend limiting consumption of red meat and choosing smaller portions and leaner cuts as ways to reduce the risk of colon cancer,” said Stephen F. Sener, MD, an Illinois surgeon and the Society’s national volunteer president. “The study reinforces the importance of consuming a mostly plant-based diet for reducing the risk of cancer. Colon cancer will kill more than 50 thousand Americans this year and addressing these needless deaths is a top priority of the American Cancer Society. Our organization believes the vast majority of those deaths could be avoided through screening and simple lifestyle changes that include moderating the amount of red and processed meat our nation consumes.”

The American Cancer Society guidelines for the early detection of colon cancer recommend that beginning at age 50, men and women follow one of the following five testing options:

• Yearly fecal occult blood test (FOBT)
• Flexible sigmoidoscopy every five years
• Yearly FOBT and flexible sigmoidoscopy every five years (preferred over either option alone)
• Double contrast barium enema every five years
• Colonoscopy every 10 years

Notes:

• Flexible sigmoidoscopy together with FOBT is preferred when compared to FOBT or flexible sigmoidoscopy alone.
• All positive tests should be followed up with colonoscopy.
• People should begin colon cancer testing earlier and/or undergo testing more often if they have any of the following colon cancer risk factors:
  • Personal history or family history of colon cancer
  • Personal or family history of intestinal polyps
  • Personal history of inflammatory bowel disease (ulcerative or Crohn’s colitis)
  • Certain genetic factors (familial adenomatous polyposis, Gardner’s syndrome, hereditary nonpolyposis colorectal cancer)

The American Cancer Society is dedicated to eliminating cancer as a major health problem by saving lives, diminishing suffering and preventing cancer through research, education, advocacy and service. Founded in 1913 and with national headquarters in Atlanta, the Society has 14 regional Divisions and local offices in 3,400 communities, involving millions of volunteers across the United States. For more information anytime, call toll free 1-800-ACS-2345 or visit www.cancer.org.