Since the 1960s, many researchers have believed that eating more fiber can help prevent colorectal cancer . Numerous studies have examined this topic, but their findings have been inconsistent. Some indicate that higher fiber intake reduces the risk of colorectal cancer, but others suggest no association.

A new study in the December 14, 2005 issue of the Journal of the American Medical Association examined data from 13 studies and found that high intakes of dietary fiber were not associated with a decreased risk of colorectal cancer.

About the Study

The researchers looked at data from 13 studies, which included 725,628 participants total. Each study used a food frequency questionnaire to assess dietary fiber intake, then followed the participants for 6-20 years, tracking who developed colorectal cancer. The researchers divided the participants into five groups (quintiles), based on their level of fiber intake.

In all studies combined, 8,081 participants developed colorectal cancer. When the researchers adjusted their findings for age and other factors affecting colorectal cancer risk (e.g., multivitamin use, folate intake, red meat intake, alcohol use), being in the highest versus lowest quintile of fiber intake was not associated with a decreased risk of colorectal cancer. But very low intake of fiber may increase the risk of cancer. Compared with people who consumed 10 or more grams of fiber per day, those who consumed less than 10 grams per day were significantly more likely to develop colorectal cancer.

This study was limited because the food frequency questionnaires used to assess dietary intake are subject to error, since people may misrepresent their food intake. Additionally, the studies only assessed fiber intake once and changing fiber intake patterns over the long term may produce different effects.

How Does This Affect You?

These findings suggest that high fiber intake may not reduce the risk of developing colorectal cancer. However, very low intakes of fiber (less than 10 grams per day) may increase the risk of developing colorectal cancer.

Does this mean that fiber is no longer an important part of a healthful diet? Absolutely not. Higher intakes of fiber are associated with many health benefits, including reduced risks of heart disease and diabetes. And future research may determine that certain types of fiber may affect colorectal cancer risk. Adults should aim to consume about 25-30 grams of fiber per day from a variety of sources. Fiber-rich foods include whole-grain breads and cereals, oatmeal, oat bran, fruits, and vegetables.