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.
References:
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
My rule is:
soluble fiber good, insoluble fiber bad.
is insoluble fiber bad and to be avoided or is just not as beneficial as commonly thought?
I get my soluble/insoluble fiber from chia.. how much fiber a day is reasonable?
Whoever imagined “bulk out our stools, give the bowel ‘something to grip on to’,” sounded like a good idea??
I’m quite happy with my small soft easily passed once a day stools thank you very much. Haven’t eaten a recognizable fiber in 2 years..
It would be helpful if we had a list of common,not exotic, foods that have a high soluble fibre content and not have to rely to rely on supplemnts and things like chia.
John, thanks for providing us with unconventional data 2010. I really appreciate your efforts.
I think there might be more this bran issue than you state, though. In this Dutch study by Simons et al. there are some confounding factors that might explain the results. The analysis included (?) also patients with Crohn’s disease and ulcerative colitis, and these patients typically have more frequent stools and more cancer. Thus, the explanation might be that IBD patients were overpresented in the increased bowel frequency group. On top of the fact that IBD patients were not excluded from the study, the investigators did not take IBD into account in the multivariate analysis either.
Here in Finland rye bread (and thus its bran) is widely consumed. Bran of the rye is fermented very slowly in colon and ferulic acid (phenol) and short chain fatty acids (SCFAs) are produced as a consequence. Intake of rye fiber is linked to imrovements of glucose and some lipid metabolism markers in clinical and experimental studies, possibly due to SCFA and ferulic acid. In some epidemiological studies intake of fiber is also linked to decreased incidence of type 2 diabetes. Grain fiber, or at least rye fiber, can potentially be protective against type 2 diabetes.
Reijo,
I sufferred from IBS for years – bloating, constipation, alternating constipation/diarrhoea. I stopped taking wheat and switched to oats and in recent years fresh sourdough wholegrain rye bread. I am astonished how well I can tolerate the rye bread – my digestion has never been better – but if a revert to wheat in more than the most minute quantities I bloat up and it can take me a week to recover. It is a great shame than rye bread is not more widely available here in the UK. Hardly any supermarkets or bakers stock it with the honourable exceptions of the most upmarket of our national full service supermarkets which stocks a choice of 2 or 3 types of fresh rye bread, and a few specialist organic bakers in London I know mine may be an isolated case but I know there has been some evidence that rye is better tolerated than wheat. If there is a problem with bran, it is a problem with modern wheat bran and not other types of bran – even spelt (ancient wheat) may be better than modern wheat.
I totally agree with Reijo that the type of bran is an issue here, and most people in the UK would be taking wheat bran. Anyone with wheat intolerance issues (most of whom haven’t realised it!)will just be making digestive problems worse by taking wheat bran. Wheat intolerance is a major factor in constipation, IBS, abdominal bloating and colitis for many people. Modern methods of high-gluten bread making are causing gluten intolerance problems which go largely undiagnosed because when tested for coeliac disease the results are usually negative.
Sadly, the advice often given by doctors for constipation and IBS is to take bran, rather than advising them to cut out wheat and eat more vegetables. Food intolerance testing is also very helpful to establish which grains can be eaten, and whether yeast or dairy intolerance is a factor. It takes the guesswork out of it.
dear dr briffa,
i enjoy your email information very much but i have to say that the article on bran or fiber is way off the mark. whatever the studies have come up with, i wonder exactly what the patients were eating. was this fiber from the factory? or the real mccoy from fresh foods? denis burkitt, as you know, found large, soft stools to be a very clear indicator of not only bowel health but, freedom from other diseases as well. i believe that this study is flawed in some way, especially the part about those who are constipated have less incidence of bowel cancer??? to be constipated means to go, but not fully, so how can this unnatural state result in a positive outcome??? for those with wheat intolerance these issues are somewhat different of course. but for the averge person, good whole fiber from a variety of foods is fundamental to good health. just my take on this mind you. keep up the good work.
sincerely,
tom dolan
The original work on this was done by? Dennis Burkitt a surgeon who worked in Africa, ( he of Burkitt’s lymphoma). He noted the high fibre diet of the natives and the low incidence of colo-rectal carcinoma and constipation.
It is very hard to believe that an increased contact of faecal matter with the mucosa, engendered by relative constipation,could result in a low incidence of cancer. This would mean that shit is good for you! The space age notion of nutri-pills would work marvellously. No more need for food.
The inclusion of cases of Crohns and Ulcerative Colitis make the study flawed for the reasons given above. I think that Dr Briffa should re-examine his theory.Fibre from vegetables other than wheat may well be better for the bowel than wheat bran, and soluble perhaps superior to insoluble fibre.
Tom and David
Burkitt’s observations have never been (to my knowledge) comfirmed. In fact, there is considerable evidence which simply does not support his theory (I referred to some of it above).
If you have knowledge of good evidence to support the theory regarding insoluble fibre and protection from colon cancer, please share it.
Often, it seems to me ‘wholewheat’ is simply made with flour that has had the bran and germ of the wheat processed out and then added back in to make a wholewheat loaf as opposed to white bread and, in many cases costing more to have this bran added back in (which had previously been taken out ?!) This denaturing and processing of grains to give us our ‘modern’ wholewheat breakfast cereals with added sugar and a few vitamins thrown in with all the advertising and marketing extolling the virtues of bran seems little more than a manufactured food and perhaps a long way from real ‘whole grains’ where no such manufacturing has taken place. My husband is extremely sensitive to foods manufactured and industrialized in this way. But we do eat, and enjoy and find healthful sourdough rye bread made by a small artisan bakery hear in San Francisco and it would appear the sourdough fermentation does help to make this bread nutritious and digestible – oh and delicious.
Sorry but at present I have no good evidence to hand re: fibre of either type protecting against colonic cancer. I was merely attempting to employ common sense. I confess to not having read Burkitt’s original work.
There is abundant evidence that a high vegetable diet, and thus one rich in fibre, offers the best basis for healthy nutrition.It also promotes more frequent bowel activation. It makes physiological sense that waste products be not retained any longer than is physically possible. Instant expelling of waste is not possible but frequent evacuations are, say 1-3 times a day. As fibre promotes this, is it not logical that it could also promote good bowel health?
As for insoluble fibre producing lacerations that could lead to over zealous tissue repair and thereby to malignancy? Sounds very fanciful to me. Can soggy, soft fibre lacerate the colonic mucosa? Even assuming it can, why should this result in cancer? Skin cells have a similar rate of turnover, I believe, to those of the gut. The part of the skin most prone to injury of any kind is that of the hands, and particularly so in manual workers. As far as I know manual workers don’t have high levels of skin cancer on their hands.
Although Dr Briffa has commented on my earlier criticism, he has not questioned the validity of a study that includes people with inflammatory bowel disease. Is he able to publish the the whole paper or would that breach copywrite?
Hi Dr Briffa,
I’m a medical student and would very much appreciate the link or name of the study demonstrating insoluble causes damage to the intestinal lining.
kind regards
sp
This was the research I was referring to:
http://www.sciencedaily.com/releases/2006/08/060823093156.htm
i WOULD LIKE TO KNOW IF PORRIDGE IS A GOOD OR A BAD THING TO EAT WITH REGARD TO FIBRE.