Diet and Colon Cancer: Meat Takes a Hit

Abstract & Commentary

Synopsis: A long-term prospective study of 148,610 adults aged 50 to 74 years showed an increased risk of colon cancer with prolonged high consumption of red meat and processed meat.

Source: Chao A, et al. JAMA. 2005;293:172-182.

The association of meat consumption and colon cancer is not new. Most studies have been observational or retrospective case-control populations, often starting with a study group having colon cancer. This study improves on previous studies by being prospective, large, and covering more than a decade (1982-1993). While not the first prospective study addressing this association, it may be the largest and longest to date.

The principal investigators of this research are with the American Cancer Society and the Rollins School of Public Health, Emory University, Atlanta. The 148,610 study subjects came from 21 states and had a mean age of 63 (range 50-74). They provided information on meat consumption in 1982 and 1992/1993 while enrolled in the Cancer Prevention Study II (CPS II) Nutrition Cohort. Follow-up from 1992/1993 through August 2001 identified 1667 incident colorectal cancers.

The relative risk of colon cancer was 1.50 for red meat consumption and 1.53 for processed meat consumption in the highest tertile groups compared with the lowest tertile eating more poultry and fish.

Comment by Joseph E. Scherger, MD, MPH

Walter Willett, MD, DrPH, from the Harvard School of Public Health, and principal investigator of the Nurses’ Health Study, provides an editorial in the same issue of JAMA reviewing this study and the general topic of Diet and Cancer.1 It is worth reading to give a historical and scientific review of this important topic (available in full text at www.jama.com). The association of colon cancer with red and processed meats has been reported since the early 1980s. Attempts to identify fat alone as the culprit have been generally negative. Proposed protective agents, such as beta-carotene and fiber, have also been disappointingly negative when studied. I think we have become more lax in dietary warnings about red meat and colon cancer; and the steak houses seem to be doing very well.

This large and important study brings this issue of red and processed meats back into concern. While a relative risk of 1.5 is not earthshaking, colon cancer is something that people want to avoid, and go to great lengths (forgive the pun) in screening.

The previous issue of JAMA had a large study from Sweden looking at the effect of high magnesium intake on colorectal cancer in women.2 Among a prospective cohort of 61,433 women aged 40-75 years, the highest quintile magnesium intake group had a relative risk of 0.59 compared with the lowest quintile. Magnesium is found in vegetables, fruits, whole grain foods and beans.

It only makes sense that what we eat will affect the health of our GI tract, especially the colon where the non-digested contents sit. Trans-fats, nitrites and other chemicals cause inflammation and oxidation of the fragile mucosa of our intestines. More often than cancer, these foods contribute to diverticulosis.

Returning to Willett, he states with extensive experience of the literature that among all the international correlations between dietary factors and various cancers, the relation between meat consumption and colon cancer has been the strongest.1 This is one piece of dietary advice we can give with assurance based on solid evidence. Fewer ribs for me in the coming months.

Dr. Scherger, Clinical Professor, University of California, San Diego, is Associate Editor of Internal Medicine Alert.

References

1. Willett WC. JAMA. 2005;293:233-234.

2. Larsson SC. JAMA. 2005;293:86-89.