Scientists have been trying to tease out the relationship between dietary fiber intake and colorectal cancer risk for years, arriving at findings that have been mostly inconclusive or contradictory. But a new analysis of existing studies adds some clarity, suggesting that consumption of fiber in the form of whole grains and cereals is strongly tied to reduced risk for that cancer.

Researchers whose work was published Thursday at sorted through data from 25 studies (involving almost 2 million participants) investigating dietary fiber intake and colorectal cancer risk. They found that high intake of fiber from whole grains and cereals was linked to a substantial reduction in colorectal cancer risk but detected no such association for fiber intake from fruits, vegetables or legumes.

For each 10 grams of total dietary fiber and cereal fiber consumed daily, they found a 10-percent reduction in the risk of getting colorectal cancer. Each three servings of such fibers consumed daily was linked to a 20 percent risk reduction; the higher the fiber intake, the lower the risk.

The study adds heft to the notion that we should add more whole grains to our diets. The 2010 Dietary Guidelines for Americans call for making half the grains we eat daily whole grains instead of refined grains. Refined grains are stripped of the fiber and many of the nutrients whole grains contain.

In addition to potentially reducing cancer risk, consumption of whole grains may lower the risk of cardiovascular disease, type 2 diabetes, overweight and obesity, and possibly overall mortality, the study notes.

The new study and an accompanying editorial suggest that fiber may reduce risk of colorectal cancer, the third most common cancer worldwide, by helping move food waste and carcinogens through our colons quickly or through other mechanisms but note that more research is needed to pin down exactly how fiber helps keep us healthy.