Whole grains, cereals, vegetables, and fruits are good sources of dietary fiber. People like Jane Stevens depend on it for a healthy diet.
"Well, I think I should be eating a fair amount of fiber," she said. "From what I understand it is good for you. It is supposed to keep cancer at bay."
Lots of people believe that eating fruits, vegetables, cereals and whole grains can reduce the risk of colorectal cancer, or cancer of the colon, the major part of the large intestine. But the results of numerous studies have been inconsistent. Some have shown a protective effect, others have shown increased risk, and still others have shown no effect at all.
A new study reported in the takes the latter position.
"We found that eating a high-fiber diet was not associated with a lower risk of colorectal cancer," said Dr. Stephanie Smith-Warner.
Dr. Smith-Warner and her colleagues at the Harvard School of Public Health in Boston analyzed 13 studies that altogether tracked the health and fiber-eating habits of more than 725,000 people in North America and Europe for up to 20 years. About 8,000 of those people developed colorectal cancer.
"We found that people who ate higher amounts of fiber had the same risk of developing colorectal cancer as individuals who ate lower amounts of fiber," she said.
It did not matter what kind of fiber. In the European studies the Harvard team evaluated, it came mostly from cereals, while fruits and vegetables were the main sources in the North American studies.
"Specifically, we found that men and women who ate at least 30 grams of fiber a day had the same risk of colorectal cancer as men and women who ate 10 to 15 grams of fiber a day," explained Dr. Smith-Warner.
But eating lots of fiber did slightly lower the risk of rectal cancer. Fiber has also been shown to help reduce heart disease and diabetes risk.
"So it is still important to eat a high-fiber diet," she said.
There are ways to reduce your risk of colon cancer. The U.S. government's Centers for Disease Control says avoid smoking, limit the amount of red meat and alcohol you consume, and exercise regularly.