Eating a diet high in fiber does not reduce the risk for developing colorectal cancer? This is the surprising finding of a recent study conducted at Harvard University.
Cancers of the colon and rectum, sometimes referred to together as colorectal cancer, are characterized by the presence of cancerous tumors in the colon or rectum, each part of the body’s digestive system. Non-cancerous tumors, called adenomatous polyps, may also grow in the colon or rectum; however, it is thought that these polyps eventually become cancerous in some persons, developing into colorectal cancer.
Researchers continue to work toward determining what factors may contribute to the development of colorectal cancer so that better treatments—and better strategies for prevention—can be produced and implemented. A person who has 1 or more characteristics, or risk factors, for a type of cancer has a higher chance to develop that type of cancer than a person who does not have these risk factors. Risk factors can be determined by studying the differences between persons who have and persons who do not have a type of cancer.
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Several risk factors have been suggested in association with colorectal cancer: age older than 40 years; a diet high in fat, protein, calories, alcohol, and meat while low in calcium and folate; a diet high in saturated fat in combination with a sedentary lifestyle; and smoking tobacco. Some have speculated that the low incidence of colorectal cancer in parts of Africa may be linked with a high-fiber diet. However, despite much focus on the possible benefits of a high-fiber diet, several studies have failed to associate such a diet with a decrease in the incidence of colorectal cancer. Researchers at Harvard University investigated the relationship, if any, between a high-fiber diet and a number of diseases, including colorectal cancer.
Harvard University researcher s studied 88,757 women, evaluating the correlation between their diet and the development of certain diseases, such as colorectal cancer, symptomatic diverticular disease of the colon, coronary artery disease, hypertension, and non-insulin-dependent diabetes. After a followup period of 16 years, the researchers found that a high-fiber diet lowered the incidence of symptomatic diverticular disease of the colon, coronary artery disease, hypertension, and non-insulin-dependent diabetes—but not of colorectal cancer. There was no evidence to suggest that increasing the dietary intake of total, cereal, fruit, or vegetable fiber is associated with a reduction in risk for colorectal adenomatous polyps or colorectal cancer. In fact, one unexpected finding was a significant increase in the incidence of colorectal cancer in those women who had a high intake of vegetable fiber. Although this association was surprising, 1 previous study did note an increased risk for colorectal cancer in persons who ate more potatoes and cruciferous vegetables.*
These researchers concluded that there are many health reasons to eat a diet high in fiber, particularly to help reduce the risk for coronary artery disease; however, such a diet does not appear to help prevent the development of colorectal polyps or colorectal cancer.
New England Journal of Medicine, Vol 340, No 3, pp 169-176, 1999) January