= Full article availableWhile dietary fiber has plenty of other benefits, it may not prevent colorectal cancer. On the other hand, eating a lot of processed meats—such as hot dogs, ham, bacon, sausage and lunch meats—probably does increase your risk of this cancer, which is second only to lung cancer as a cause of cancer deaths. But the good news is that—for reasons scientists can’t yet explain—eating chicken seems to be associated with a reduced risk of colorectal cancer.
Those are the sometimes-surprising findings of two new studies of diet and the risk of cancer of the colon or rectum, which kills 56,000 Americans annually. The first study, an analysis of the combined data from 13 previous studies involving 725,628 men and women and ranging from six to 20 years, was published in the Journal of the American Medical Association (JAMA). Close on its heels came the publication of a second study of 1,520 participants in two randomized trials, the Antioxidant Polyp Prevention Study and the Calcium Polyp Prevention Study, in the American Journal of Gastroenterology. All 1,520 subjects had a recent history of benign colorectal tumors called adenomas; the adenomas were removed, and patients got follow-up colonoscopies one and four years later.
The JAMA meta-analysis did find a significant benefit for fiber after adjusting only for subjects’ ages. But after taking into account other dietary factors, such as folate intake, red-meat consumption and alcohol use, that benefit all but disappeared from the data. Contrary to some other findings on fiber and colorectal cancer, the conclusion was that the association was not statistically significant.
That’s no reason to stop consuming fiber, however. The researchers—led by Yikyung Park, DSc, of the Harvard School of Public Health, now a visiting fellow at the National Cancer Institute—noted that benefits have been found for fiber from whole plants against an array of other disorders, including diabetes and heart disease.
“Colorectal cancer arguably has the most confusing association with fiber,” noted John A. Baron, MD, of Dartmouth Medical School, in an accompanying editorial. Further research will be needed to sort out this confusion and the conflicting studies, Dr. Baron wrote.
The second new study, authored by Douglas J. Robertson, MD, MPH, also of the Dartmouth Medical School and of White River Junction VA Medical Center, was similarly discouraging about fiber’s protective powers. Only a weak, non-significant association was found between fiber intake and reduced risk of recurrent adenomas, although a stronger benefit was seen against recurrence in the proximal colon. The strongest association with reduced risk was seen for fiber from vegetables and fruit and for fiber from grains.
On the flip side, subjects who ate the most processed meats had a 75% greater risk of advanced adenoma recurrence than those who ate little or no processed meat. The researchers fingered a possible increase in carcinogens in meat from salting, smoking or adding nitrates as the likely culprit.
The study found no added risk from consuming red meat, unlike some previous research, or fat.
Perhaps the most surprising result, however, was a beneficial association with eating chicken. The subjects who ate the most chicken had a 39% reduced risk of adenoma recurrence compared to the group consuming the least chicken.
“The mechanism by which poultry intake would independently reduce colorectal cancer incidence is not clearly delineated,” the researchers wrote. “Poultry is a minor source of the nutrients selenium and calcium that have been associated with decreased risk for colorectal cancer.”
In any case, they noted, the study suggests that some of the dietary guidance given to fight heart disease may also be good advice against colorectal cancer: Cut down on processed meats and include lean meat such as chicken (without the skin) in a balanced diet.
To learn more: Journal of the American Medical Association, Dec. 14, 2005. American Journal of Gastroenterology, Dec. 2005 (click abstract for 2789). American Cancer Society.
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