Fermentable Carbohydrates May Cause or Aggravate Irritable Bowel Sydrome

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

Irritable bowel syndrome (IBS) is one of the conditions that allegedly improves with a paleo diet. It’s frustrating for sufferers and their doctors. My ears perk up when I hear about a new treatment.       

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 a few years ago. That alone has at least potential to reduce IBS symptoms. (I eat more than 50 g a day now.)

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.) Some of the aforementioned foods are restricted or forbidden on the paleo diet.

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.

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 About.com says the diet should be undertaken only with the supervision of a qualified nutritionist.

BTW, I’m not aware of any scientific reports looking at the paleo diet as a treatment for IBS. If it works for you, stick with it.

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)