High-Fiber Diet May Not Reduce Colon Cancer Risk
ATLANTA--In the April 20 edition of The New England Journal of Medicine, two large studies found that a high-fiber diet may not protect against colon cancer. Previously, studies had suggested that a diet high in fiber could reduce a person's risk, but research had not directly measured the anti-cancer effects of a high-fiber diet.
"There may be reasons to eat a diet that is low in fat and high in fiber, fruits and vegetables or to supplement the diet with a food high in cereal fiber," said Tim Byers of the University of Colorado School of Medicine. "Preventing colorectal adenomas, at least for the first three to four years, is not one of them."
Colorectal adenomas--polyps that can turn into tumors--gauge the effectiveness of a high-fiber diet because they appear faster, while colorectal cancer itself can take years to develop.
In the first study, conducted at the National Cancer Institute (NCI), 958 people were put on low-fat, high-fiber, high-fruit and vegetable diets. Another 947 people were given information on eating healthy and were told to follow their usual diets. All participants had at least one pre-cancerous polyp removed in the six months prior to the study. After four years, researchers found that both groups had the same chances of developing another polyp.
In the second study, conducted at the Arizona Cancer Center, 719 people ate half an ounce of wheat bran fiber each day, while another 584 ate less than a tenth of an ounce. After three years, colonoscopies found that the risk of developing a polyp was the same for both groups.
Some researchers believe three and four years was not a long enough time to observe the groups. "All the NCI study says is that at one stage over a four year period of time, the diet had no effect," said Dr. Moshe Shike of Memorial Sloan-Kettering Cancer Center. "Cancer, particularly colon cancer, may take 15 years to develop." Also, because the average age of the NCI study participants was 61, these findings may show that dietary changes need to be made earlier in life.
A high-fiber diet can still reduce the risk of heart disease, high blood pressure and diabetes. For further information, visit www.nejm.org/context/2000/0342/0016/1149.asp.