Dietary Fiber Lowers Colon Cancer Risk

Laurie Barclay, MD

May 01, 2003

May 1, 2003 — Two studies reported in the May 3 issue of The Lancet further support that high-fiber diets do indeed reduce the risk of colon cancer, contrary to the results of some recent studies.

"Dietary fibre, particularly from grains, cereals, and fruits, was associated with decreased risk of distal colon adenoma," write Ulrike Peters, from the National Cancer Institute in Rockville, Maryland, and colleagues.

In the randomized Prostate, Lung, Colorectal, and Ovarian (PLCO) Cancer Screening Trial, the investigators used a food frequency questionnaire to compare fiber intake of 33,971 subjects who did not have polyps on sigmoidoscopy with that of 3,591 subjects who had at least one adenoma in the distal large bowel (descending colon, sigmoid colon, or rectum).

After adjustment for potential dietary and nondietary risk factors, high intake of dietary fiber was associated with a lower risk of colorectal adenoma. Participants in the top quintile of dietary fiber intake had a 27% lower risk of adenoma than those in the lowest quintile (95% confidence interval [CI], 14% - 38%; P = .002). Compared with the lowest quintile, those in the top quintile had an increase in fiber intake of 24 g per day.

Although risks were similar for advanced and nonadvanced adenoma, fiber intake did not affect risk of rectal adenoma. "Finding an inverse association for small (non-advanced) adenoma suggests that high-fiber diet is protective from the earlier stages of adenoma formation," the authors write.

In the second study, Sheila A. Bingham, PhD, and colleagues from the European Prospective Investigation into Cancer (EPIC) prospectively examined the association between dietary fiber intake and incidence of colorectal cancer in 519,978 individuals aged 25 to 70 years, recruited from 10 European countries.

After an average follow-up of 4.5 years, there were 1,065 diagnoses of colorectal cancer. Risk of colorectal cancer was 25% lower in subjects in the top quintile for fiber intake than in subjects in the bottom quintile (adjusted relative risk, 0.75; 95% CI, 0.59 - 0.95). Mean fiber intake was 35 g in the top quintile and 15 g per day in the bottom quintile. As in the other study, fiber intake did not protect against risk of rectal cancer.

"No food source of fiber was significantly more protective than others," the authors write. "In populations with low average intake of dietary fiber, an approximate doubling of total fiber intake from foods could reduce the risk of colorectal cancer by 40%."

Lancet. 2003;361:1491-1495, 1496-1501

Reviewed by Gary D. Vogin, MD

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