Thursday, November 17, 2011

Fiber From Whole Grains May Protect Against Colorectal Cancer

A new large analysis (~2 million people) investigating the link between dietary fiber and colon cancer:

Dietary Fibre, Whole Grains, And Risk Of Colorectal Cancer: Systematic Review And Dose-Response Meta-Analysis Of Prospective Studies, British Medical Journal, November 2011

Found that:
"A high intake of dietary fibre, in particular cereal fibre and whole grains, was associated with a reduced risk of colorectal cancer."
Interesting ... Fruits, vegetables, and beans were not as protective as whole grains:
"Our meta-analysis supports an inverse association between intake of dietary fibre, cereal fibre, and whole grains and risk of colorectal cancer, but we found no significant evidence for an association with intake of fibre from fruit, vegetables, or legumes."
How much:
"Our results indicate a 10% reduction in risk of colorectal cancer for each 10 g/day intake of total dietary fibre and cereal fibre and a about a 20% reduction for each three servings (90 g/day) of whole grain daily, and further reductions with higher intake."
What kind:
"Total whole grains included whole grain rye breads, whole grain breads, oatmeal, whole grain cereals, high fibre cereals, brown rice, and porridge."
Dagfinn Aune, lead study author:
"The more of this fibre you eat the better it is. Even moderate amounts have some effect."
- Fibre And Whole Grains 'Reduce Bowel Cancer Risk,' BBC, November 10, 2011
That same BBC article said:
"The lifetime risk of being diagnosed with colorectal cancer in the UK is estimated to be one in 14 (6.9%) for men, and one in 19 for women (5.4%)."
Wow, those are some risks.

Update, November 17:

I'm adding a graph from the study and an excerpt from their "Mechanisms" paragraph. The graph shows a statistically significant and linear inverse association ... as fiber intake went up, cancer risk went down.


Dietary fiber:
"... may decrease the risk of colorectal cancer by increasing stool bulk, diluting faecal carcinogens, and decreasing transit time, thus reducing the contact between carcinogens and the lining of the colorectum. In addition, bacterial fermentation of fibre results in the production of short chain fatty acids, which may have protective effects against colorectal cancer."
These mechanisms aren't new to this blog, e.g. transit time and dilution. The interaction of fiber with colonic bacteria is notable. I saw this benefit with resistant starch too. (See Resistant Starch May Reduce Risk Of Colon Cancer.) Resistant starch isn't fiber per se; it's a vegetable starch that fails to get digested and ends up in the colon where bacteria feed upon it. I've written about it here.


Bix said...

I wanted to say about this study...

It may well be that fiber (if that's indeed the acting substance) is mitigating the effect of something else they are eating, either by increasing transit time or interacting with gut flora. We know that for some people, foods that cause the release of a lot of bile (fatty foods) irritate the colon. We know that processed meat show up time and again as linked to colon abnormalities. So ... if you could find out what food is problematic, and minimize it, then the benefit you see with cereal fiber may be reduced.

This is a difficulty with nutritional reductionism. That is, with investigating the effect of a nutrient in isolation.

pronutritionist said...

Yes, this is an interesting study. I also wrote about it. A bit concerning is that the authors do not refer to a Cochrane database meta-analysis that showed no effect of fiber in RCT setting.

You mention resistant starch. I agree, it is important. In addition, it is also all the other poorly digestable carbohydrates that might be of important, such as polyols (sorbitol, xylitol, ect.), fructans, galactans, even fructose and lactose. These are all fermented to some degree in large bowel and may bring about health benefits in many disease areas but not in IBS.

Dietitian Reijo L