Fiber in the diet affects men and women differently
Posted by Kate Murphy on February 23rd, 2006
The affect of dietary fiber has been controversial in preventing colorectal cancer. Observations of colorectal cancer rates in cultures where larger amount of fibrous food are eaten compared to Western diets led to theories that fiber might protect against the development of cancer.
However, no clear connection between the amount of fiber in the diet and the incidence of polyps or cancer has been found in a number of studies. In a new analysis combining two previous studies that looked risk for colon polyps for men and women separately shows that fiber may help men, but not women. The combined results were published in the February 2006 American Journal of Clinical Nutrition.
Researchers combined information from groups in both the Wheat Bran Fiber Study and the Polyp Prevention Trial. Together there were about 3,200 participants who had pre-cancerous polyps (adenomas) removed during a baseline colonoscopy. They were randomly assigned to either their usual diet or a high-fiber intervention diet with a follow-up colonoscopy 2–4 years later.
Although there was no significant difference overall between participants who had followed an enriched fiber diet and those who did not the team did find that men had about a 20% reduction in recurrent polyps. There was no similar difference for women.
The Wheat Bran Fiber Study design actually provided either a high-fiber or low-fiber cereal for participants. However, when results were published in the New England Journal of Medicine in April 2000, there were no significant differences between the two groups in those who had new polyps and those who didn’t. The team did notice a difference for men, but given the number of male participants enrolled, this could have been due to chance.
In the Polyp Prevention Trial participants were randomly assigned to an intervention group that received nutrition counseling and were advised to eat a low-fat, high-fiber diet with with at least 3 1/2 servings of fruits and vegetables each day. Both groups had about a 40% chance of having another polyp during the 4 year follow-up period, although most polyps were small. About 5% in each group had an adenoma larger than 1 centimeter. For whatever reason, there were more colorectal cancers found in the intervention group (10) than in the control group (4). The full report of the trial from the New England Journal of Medicine is online.
Read an article about the new analysis from Reuters.
Additional information about the Wheat Brain Fiber Study and the Polyp Prevention trial is available from the National Cancer Institute web site.
