The Low FODMAP Diet Approach: Effects of FODMAPs on the Gut

Effects of FODMAPs on the Gut – Fluid Changes and Production of Intestinal Gas

There is new evidence that suggests that the benefits of a particular diet depend on the gut microbial composition. We need a better idea of what a specific diet does to the gut microbes and microbial metabolites, and how these substances affect the nervous system in the gut and brain

FODMAPs are types of carbohydrates found in foods like wheat and beans. IBS patients who follow the low FODMAP diet eat less of the fiber that supports beneficial microbes in the gut. In the short term, a diet like this may lessen
symptoms for some IBS patients. Still, these diets are difficult to maintain for a long time, and they may even have adverse effects on gut microbiota. Moreover, it
appears that a healthy, balanced microbiota also can alleviate symptoms. So, a low FODMAP diet may not be the best choice for managing IBS.

In the small and large intestine, the small FODMAP molecules exert an osmotic effect, which means more fluid is drawn into the bowel. FODMAPs are also rapidly fermented by colonic microflora producing gas. The increase in fluid and gas distends the bowel. This can cause the sensation of bloating and abdominal pain or discomfort and affects how the muscles in the wall of the bowel contract. It may cause increased forward movement (peristalsis) leading to diarrhea, but in some people, it can cause constipation.

It is important to appreciate that malabsorption of FODMAPs occurs to the same extent in healthy people and is a normal phenomenon. It is only in irritable bowel syndrome (IBS) that gut symptoms are induced more readily. The reasons for this may include:

  1. The way the muscles of the bowel respond (motility) to the distension: They could result in a faster or slower passage through the gut.
  2. The gut is “hypersensitive” to changes in the gut environment and to interactions with the nervous system and immune system within the digestive tract: This means that IBS individuals are more likely to perceive pain at a lower threshold when distension of the bowel is present compared to healthy adults.
  3. The type of bacteria in the bowel: The bowel bacteria might produce larger amounts of gas or there may be increased bacterial numbers in the small intestine (called small intestinal bacterial overgrowth or SIBO) so that more gas is produced in the small bowel. Distension of the small bowel can cause increased abdominal discomfort, distension, and bloating.

Adapted from IFFGD Publication #251 by CK Yao, Jessica Biesiekierski, Sue Shepherd, Peter Gibson, Eastern Health Clinical School, Monash University, Box Hill Hospital, Melbourne, Australia and Adapted from IFFGD Publication #273 “Functional GI Disorders, Microbes, and Brain-Gut Interactions” by Cole W. Norton and Aki S. Norton, IFFGD, in collaboration with Emeran Mayer Adapted by Abigale Miller.

Last modified on September 2021

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IFFGD is a nonprofit education and research organization. Our mission is to inform, assist, and support people affected by gastrointestinal disorders.

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