By David
Brown
Washington Post Staff Writer
Thursday, January 21, 1999; Page A3
Eating a diet high in fiber doesn't lower a woman's risk of developing cancer of the colon or the rectum, according to research published today.
A study of 88,000 women, whose health and diets were followed for 16 years, found that those who ate a relatively small amount of fiber had the same risk of colorectal cancer as those eating more than twice as much.
The theory that diets high in fiber protect against colorectal cancer was first seriously propounded 30 years ago. Fiber is the structural material of plants that can't be absorbed by the human digestive tract. Contrary to many public perceptions, however, evidence for the theory has been sketchy at best.
"My own conclusion is that if one is concerned about preventing colon cancer, I'm not sure that [consuming] fiber is an effective method," said Charles S. Fuchs, a physician at Brigham and Women's Hospital in Boston, who headed the study. "But there are many other potentially effective ways to do that."
Exercise lowers the risk for colon cancer, as does the regular use of aspirin. Eating red meat tends to raise it. There is some evidence that obesity, as well as consumption of fat and sugar, also raises the risk.
As with most epidemiological studies, it's impossible to say with certainty whether these results are correct. A more definitive test of the theory is to randomly assign people to follow either a low-fiber diet or a regular diet, and then observe them for cancer. At least two such studies are underway.
Previous studies have shown that high-fiber diets help protect against coronary heart disease, hypertension, diabetes and a relatively rare disease of the colon called diverticulitis.
"I think it's still important to eat a high-fiber, low-fat diet," said Robert Kurtz, chief of the gastroenterology and nutrition service at Memorial Sloan-Kettering Cancer Center in New York. "I think we'll all be healthier for that. Will it protect against colon cancer? We don't know yet."
Colorectal cancer is the third most common form of cancer, in terms of new cases and deaths, in the United States. Colon cancer is more common than rectum cancer, and accounts for 85 percent of colorectal cancer deaths.
The findings, published in today's New England Journal of Medicine, came from the Nurses' Health Study, which has regularly queried about 121,000 American nurses (starting in 1976), and then monitored their health.
In 1980, 1984 and 1986, the women filled out questionnaires in which they estimated how frequently in the previous year they ate dozens of different foodstuffs. The amount of fiber, and many other nutrients, in each woman's daily diet was then calculated. (The researchers compared the data with actual measurements of the foods consumed -- measurements that a small subgroup of women did for a month. The questionnaire proved to be an adequate, although not perfect, method of gauging actual intake.)
The women were then divided into five groups. The group with the lowest intake consumed about 10 grams of fiber a day, the group with the highest consumed about 25 grams.
By 1996, there were 787 cases of colon or rectum cancer among the women. There was no significant difference in the rates of cancer between any of the groups. The researchers made statistical adjustments to compensate for other possible risk factors, such as physical activity, alcohol intake and fat consumed. There was also no relationship between fiber intake and the development of adenomas, the type of colon polyp from which nearly all cancers arise.
Although the study involved only women, previous research had raised questions about whether fiber reduced the risk for colorectal cancer in men, the researchers said.
Screening for colon polyps or cancers is the most certain way of reducing one's risk of dying from the disease. People whose colorectal cancers are discovered before they experience any symptoms have a 90 percent chance of living five years. If the cancers are found only after they have become large enough to cause symptoms, the five-year survival rate drops to about 50 percent.
Although the salutary effects of raw vegetables and fruits have been mentioned since ancient times, the theoretical link between fiber and colon cancer was first suggested in 1969 by a British surgeon named Denis Burkitt.
A Presbyterian medical missionary who spent two decades in Uganda, Burkitt noted the extreme rarity of colon cancer among his African patients. He theorized that their high-fiber diets were the reason.
Subsequently, researchers theorized that fiber might protect against cancer by neutralizing cancer-causing substances in the digestive system or by speeding the digestive process, reducing exposure to those substances.
© Copyright 1999 The Washington Post Company
