FODMAPs (an acronym for “fermentable oligosaccharides, disaccharides, monosaccharides, and polyols) are short-chain carbohydrates.   They are difficult for the small intestines to absorb, so they are fermented by the microbiota in the large intestines of those with IBS.  As this occurs, gas is produced by the microbiota, causing the person to feel gassy, bloated, and perhaps to have a stomach ache.  Additionally, FODMAPs increase the amount of fluid inside of the small intestine and colon, which sometimes leads to loose stools.

People with IBS have lower amounts of digestive enzymes present and/or difficulty transporting nutrients, which makes the FODMAP absorption process even more difficult.  When FODMAPS are reduced in the diet, bloating, gas, stomach pain, and diarrhea are significantly reduced. Additionally, because the low FODMAP diet is not hugely limiting, people are more likely to stay consistent with following it over a long period of time (Nanayakkara, et al., 2016).

Reference

Nanayakkara, W.S., Skidmore, P.M., O’Brien, L., Wilkinson, T.J., Gearry, R.B. (2016). Efficacy of the low FODMAP diet for treating irritable bowel syndrome: the evidence to date. Clinical and Experimental Gastroenterology, 9, 131-142.