Does Diet Affect Irritable Bowel Syndrome?

"Dr. Parker, what can I do about these severe belly cramps?"

“Dr. Parker, what can I do about these belly cramps?”

Four weeks of fermentable carbohydrate restriction reduces symptoms of irritable bowel syndrome, according to UK and Australian researchers.

Here’s the theory of how it works.  Our intestines—colon, mostly—are loaded with bacteria.  The food you feed your bacteria—fermentable carbohydrates, for example—may have an effect on the bacteria.  Changes in bacterial populations in response to feeding, in turn, may lead to changes in irritable bowel syndrome and other aspects of health.  This “gut microbiome” is a hot area of research and speculation.

I don’t have irritable bowel syndrome (IBS), but did notice a major decrease in gastrointestinal gas production when I reduced my digestible carbohydrate consumption to less than 50 g/day.  That alone has at least potential to reduce IBS symptoms.

IBS is extremely common, affecting 10–15% of individuals in the developed world. Only 15% of those bother to seek medical attention. Of all referrals to gastroenterologists (stomach specialists), at least 25% are for IBS.  There are few reliable treatments and cures. In some cases it mysteriously resolves on its own.

So I got excited when I ran across the study I reference above.  I’m not going to spend a lot of time on it because I’ve already spent too much trudging through the article, and I don’t have much to show for it.

The way the investigators wrote their report gave me some heartburn:

  • They never bothered to define “fermentable.”  In this context it probably refers to digestion or breakdown of food by gut bacteria rather than by human hosts.
  • They never bother to spell out exactly what foods the experimental subjects were eating as they restricted fermentable carbohydrate consumption.
  • The intervention group (n=19) was instructed to restrict foods “high in fructans (e.g., wheat products, onions), galacto-oligosaccharide (e.g., legumes), polyols (e.g., pear, sugar-free gums), lactose (e.g., mammalian milk), and excess fructose (e.g., honey).”  Does “restrict” mean “cut back a little” or “avoid entirely upon penalty of death”?  Your guess is as good as mine.  (It’s a joke—I know they wouldn’t kill’em.)

Have you heard of FODMAPs?  That seems to be the intervention diet that restricted fermentable carbohydrates. FODMAP stands for fermentable oligosaccharides, disaccharides, monosaccharides, and polyols.

You need a break. Enjoy.

You need a break. Enjoy.

Let me summarize their results simply by saying they found changes in gut bacteria and a reduction in irritable bowel syndrome symptoms, as compared with control subjects.  The particularly responsive symptoms were bloating, borborygmi, and the urge to defecate.  Abdominal pain strongly tended to improve but didn’t quite reach statistical significance.  Diarrhea wasn’t affected.  Also note that the IBS patients allowed into the study were not the type with constipation as a major issue.

So What? 

If you want to try a FODMAP diet for your IBS, you won’t be able to figure out what to eat based on this report. Consult your own physician about it. I wonder whether many of them have even heard of FODMAP.  Barbara Bolen, Ph.D., at says the diet should be undertaken only with the supervision of a qualified nutritionist.

Steve Parker, M.D.

Reference:  Staudacher, Heidi, et al.  Fermentable Carbohydrate Restriction Reduces Luminal Bifidobacteria and Gastrointestinal Symptoms in Patients with Irritable Bowel Syndrome.  Journal of Nutrition, 142: 1520-1518 (2012)


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2 responses to “Does Diet Affect Irritable Bowel Syndrome?

  1. Buzz

    I would like to comment on this as I have IBS (Diahhrea predominant), have done a great deal of personal research into IBS, and my own gastroenterologists specialize in functional digestive disorders as well as do research into IBS.
    The FODMAP diet is the current “diet of suggestion” by the specialized medical community. It is basically a low carb, low sugar diet with quite a few vegetables included. (BTW, the reason they say it should only be done under the supervision of a qualified nutritionist is the same reason they would say your diet should be done under supervision–too much fat, no beans, no whole grains, no fruits, limited vegetables, now, the old mantra.)
    Over ten years ago, my own doctors told me to try an Atkins-style diet because they saw, in clinic, the best results from that type of diet for IBS-D patients.
    Personally, I can say that if I indulge in your basic starches or sugars, I have a better chance of having IBS problems.
    If you want a better understanding of what you can and can’t eat under FODMAP, try this site:

    Click to access DH-Low-FODMAP-Diet-Handout.pdf

    The question, “Does Diet Affect IBS….well, for some, it does. For others, it doesn’t.