Think bran is good for the bowels? Think again

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My blog on Christmas eve (My nutritional Christmas wish list) detailed 14 things I feel should be more widely known including the facts that saturated fat is not linked in any meaningful way with heart disease and there’s no good evidence that margarine is healthier than butter. Another was that there’s no good evidence that insoluble fibre has any benefits for health. I know our doctors (even me at one time), dieticians and health agencies insist that bran is ‘good for bowel health’, but it’s just one of those nutritional memes myths that started as a theory and then somehow got stuck. And the problem with such myths is that once they have stuck, they can be very difficult to un-stick.

All we can do, in this situation, is highlight the lack of scientific validity of these sorts of ideas. While we’re unlikely to change the opinions of many health professionals, researchers and our Governments any time soon, the presenting of the evidence does at least give interested members of the public an opportunity to see the other side and at least make their own minds up.

To this end, I’m going to devote today’s blog to some recent research relating to fibre and the bowels. Before I do, I just want to run over what conventional ‘wisdom’ tells us about this.

There are two sorts of the fibre in the diet: insoluble and soluble. Insoluble fibre is found in things like wholemeal bread and bran-rich breakfast cereals. This ‘roughage’ is believed to bulk out our stools, give the bowel ‘something to grip on to’, and speed up the time it takes for faeces to be eliminated as well as reducing any risk of constipation. I remember learning at medical school that there were elements in faeces that could induce cancerous changes in the colon wall. The more briskly the feaces moved through the colon, we were told, the less likely the faeces is to exert any cancerous process.

However, like a lot (? most) of what I was taught at medical school, this turned out to be unfounded. It’s not like, by the way, that there was good evidence for this to begin with and then more contemporary evidence disproved it. The fact is, there never was any good evidence for this idea.  And when the evidence that sought to prove it came up negative [1-3] the idea still managed to persist.

More evidence for the lack of benefits from fibre came from a recent Dutch study that compared the fibre intakes and risk of colon cancer (technically referred to as ‘colorectal’ cancer) in men [4]. Basically, fibre content in the diet, in this study, had no relationship with colorectal cancer risk. No surprises here, as it’s in keeping with previously-published research.

What was a bit more surprising about this study is the relationship between constipation and cancer risk. Remember, we’re told that constipation is a likely risk factor for colon cancer and preventing constipation (with a yummy bran-rich cereals) is a must here.  Well, the results of this new study did not support this idea at all. In fact, men who reported suffering from constipation at least sometimes were, compared to those who were never constipated, at a 24 per cent reduced risk of colorectal cancer. Risk of rectal cancer was down by 43 per cent.

And here’s another thing, increased bowel frequency was associated with an increased risk of cancer. Individuals having 1-2 bowel motions a day (compared to those having movements once a day only) were found to be at 29 and 50 per cent increased risk of colorectal and rectal cancer respectively.

Now, epidemiological studies of this nature can really only tell us about associations between things, and not whether one thing is causing another. In other words, we don’t know whether constipation and less frequent bowel motions protect against colon cancer, only that these things are associated.

Do bear in mind though that insoluble fibre has been show to induce tiny rips and tears in the lining of the bowel. These will need repairing of course, requiring proliferation of cells. Uncontrolled cell proliferation, by the way, is the hallmark of cancerous tumours. While doctors, dieticians and cereal manufacturers often extol the virtues of bran, my opinion is that such foods should be flushed (straight) down the toilet.


1. Fuchs CS, et al. Dietary fiber and the risk of colorectal cancer and adenoma in women. N Engl J Med. 1999;340(3):169-76

2. Jacobs ET, et al. Intake of supplemental and total fiber and risk of colorectal adenoma recurrence in the wheat bran fiber trial. Cancer Epidemiol Biomarkers Prev. 2002 11(9):906-14

3. Alberts DS, et al.  Lack of effect of a high-fiber cereal supplement on the recurrence of colorectal adenomas. Phoenix Colon Cancer Prevention Physicians’ Network N Engl J Med. 2000;342(16):1156-62

4. Simons CCJM, et al. Bowel Movement and Constipation Frequencies and the Risk of Colorectal Cancer Among Men in the Netherlands Cohort Study on Diet and Cancer. Am J Epidemiol 2010;172(12):1404-14

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