Friday Focus: Fiber and Colorectal Cancer Prevention

haricot beans, lentil and riceToday kicks off National Colorectal Cancer Awareness Month, and you’ll be hearing a lot about the diseases’ symptoms, risk factors and screening guidelines in the news. This is only as it should be; these messages need to get out there and be heard if we hope to raise awareness of colorectal cancer, increase its early detection, and ultimately save lives.

But there’s a vital message that doesn’t make the headlines, a key component of colorectal cancer prevention that too often gets lost in the focus on screenings and symptoms.  And that’s this:

We can cut the number of colorectal cancers in half. Starting today. Simply by making healthier everyday choices.

Throughout March, the AICR Blog will set aside each Friday to focus on one of those healthy changes. Today, let’s take a closer look at the evidence on fiber and colorectal cancer risk.

What’s The Link?

Only plant foods (vegetables, fruit, whole grains, beans and nuts) contain fiber.

Back in 2007, the AICR/WCRF expert report collectively analyzed evidence from thousands of studies and concluded that foods containing fiber are protective against colorectal cancer. Specifically, the AICR/WCRF experts judged that there was sufficient evidence that a probable causal relationship exists between these foods and protection against colorectal cancer.

But something happened last year, when we published our AICR/WCRF Continuous Update Project (CUP) report on colorectal cancer. The CUP report examined all relevant evidence on colorectal cancer, including new studies since our expert report was published.

The evidence that fiber-rich foods protect against colorectal cancer got stronger. So strong that the CUP Panel upgraded the evidence to convincing, the most stringent judgment possible.

Now, as far as the take-home message goes, it’s not a change: Basically, any link that earns a panel judgment of probable or convincing becomes part of AICR’s Recommendations.

But it’s significant, because it means we can feel even more confident that diets high in plant foods are protective against colorectal cancer.

Why is Fiber Protective?

Fiber is the part of the plant our body doesn’t digest, the part that passes through you, doing good, protective work as it goes. Plant foods contain both soluble fiber (which dissolves in water) and insoluble fiber (which doesn’t.) Both kinds are protective, because they:

  • Slow digestion, so you feel full longer, which helps protect against overeating
  • Help lower blood sugar levels, which aids insulin sensitivity
  • Dilutes substances in food which could damage the colon, and ushers them out of the body more quickly
  • Protects the lining of the colon
  • Helps produce gut substances like butyrate, a fatty acid which may help defend against cancer

It’s important to note that the evidence that fiber is protective involves fiber-rich plant foods, not fiber supplements. Pills and powders are no match for the protective power of the overall diet.

Fiber-rich foods join the select group of other colorectal links that received a grade of convincing from the CUP Panel:

  • Physical activity is protective.
  • Red and processed meat raise risk.
  • Alcoholic drinks raise risk.
  • Carrying excess body fat raises risk.

Next Friday: Why moving more protects against colorectal cancer.