People who eat high-fiber diets run a lower risk of colorectal cancer than those who don’t -- but it’s probably not the fiber that’s protecting them, scientists report today in one of the largest studies of the subject.
Researchers seeking to resolve one of the most controversial issues in cancer prevention found that colorectal cancers were 16% less common among people consuming the most fiber than among those receiving the least.
But the advantage probably comes from other healthy lifestyle choices made by the fiber eaters, who tend to smoke less, exercise more, avoid red meats and consume more fruits, vegetables, whole grains, calcium and folic acid, the researchers said.
When researchers controlled for these factors, evidence of fiber as a cancer fighter disappeared.
The researchers, mainly from the Harvard School of Public Health and affiliated institutions, pulled together 13 previous studies that tracked 725,000 men and women for six to 20 years.
Their report, appearing in the Journal of the American Medical Assn., is the third major study in six years to cast doubt on decades of claims made by health advocacy groups, cereal companies and nutritionists that fiber was a key to preventing colon cancer.
“People who eat high fiber tend to have a healthier lifestyle and a more healthy diet,” said Yikyung Park, an epidemiologist with the National Cancer Institute. “Those things together may reduce the risk of colon cancer.”
Colorectal cancer, a term that encompasses tumors of the colon and rectum, is the nation’s second-leading cancer killer, claiming 56,000 lives last year. Only lung cancer killed more.
But the debate over fiber is unlikely to end here. A large European study of half a million people followed for more than a decade recently found a statistical link between high-fiber diets and a lower risk of colorectal cancer.
“There is still a controversy,” Park said. “We need to look into more specifics, like the types of fibers people eat, the sources of fiber and whether people with certain characteristics may have some benefit.”