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Fermentation and FODMAPs

What is fermentation and why should you care? If you have IBS or suffer from excess flatulence, bloating, or gassy abdominal pain, knowing a little bit about fermentation might help you get more benefit from your FODMAP elimination diet.

The gastrointestinal tract is populated by billions and billions of microorganisms, including bacteria and archaea. That is normal. Fermentation is the process that occurs when these microbes consume and break down carbohydrates. The microbes need energy to survive, and they get it by eating your lunch; any carbohydrates in your food that you don't digest and absorb get passed along to gut microbes. In the process of fermentation, microbes produce hydrogen, methane and other gases. The gases make the intestines expand; picture a tube-shaped balloon expanding as it is blown up. The abdominal wall gently expands to accommodate this, and the gas is eventually either passed as flatus or absorbed into the blood stream. That's all normal, too. But for unknown reasons, in people with IBS, the expansion of the intestine is sometimes experienced as a painful sensation. What is it about FODMAPs that make fermentation a problem for some people?

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  • Rapid fermentation. Some carbohydrates are fermented more rapidly than others, such as those that are defined as FODMAPs; a diet loaded with FODMAPS might cause rapid gas production. Rapid gut distension could follow. Excess gas production could be a problem too.
  • Poor absorption. Lactose and fructose (FODMAPs, again!) can be poorly absorbed by some people, which presents extra food to the intestinal bacteria. No one fully absorbs sugar alcohols like mannitol and sorbitol. And fiber is never digested or absorbed by humans--that's part of what defines them as fiber!
  • Fast intestinal transit time due to a virus, inflammatory bowel disease, celiac disease or non-FODMAPs food sensitivity. If the dietary carbohydrates are rushing past your small intestine before they can be absorbed, again, excess food may be presented to the bacteria in the large intestine.

It stands to reason that limiting rapidly fermentable carbohydrates (FODMAPs) would cut down on sharp increases in gas production. We wouldn't want to squelch fermentation altogether, though, as it is a normal part of human physiology, and some of the products of fermentation are good for us. That's one reason that the FODMAP elimination phase of the diet is meant to be short, and that long term I encourage my patients to consume as much FODMAP fiber as they can tolerate. Again, it is normal to produce some gas and to pass gas, even many times a day, as long as it is not causing pain or distress.

What else can you do to make yourself more comfortable?

  • Avoid clothes with tight waistbands. Tight clothing can prevent the natural expansion of the abdominal wall to accommodate gas production via fermentation--sorry if this sounds harsh,  but consider this one if you've gained a few pounds and are still trying to fit into your skinny clothes.
  • Traveling in a car or airplane or nearby other people at work? Maybe you are holding on to some of that gas you should be passing. Time for a quick walk around the block or a quick trip to get something out of your car in the company parking lot--whatever it takes to get a little privacy so you can let 'er rip.
  • Can't pass that gas? Take a yoga class and ask the teacher (privately ;)) to suggest and demonstrate several gas-releasing poses.