"In healthy individuals, FODMAPs may cause a little more flatulence, but not pain, diarrhea, and bloating," says William Chey, a gastroenterologist at the University of Michigan who studies the low FODMAP diet. FODMAPs also trigger abnormalities in how IBS patients' bowels function, Chey adds. For example, their colons may be hyperactive after a meal, and FODMAPs might exacerbate that activity.
FODMAPs also seem to influence the microbes living inside the gut. Recently, a team led by Chung Owyang, another gastroenterologist at the University of Michigan, reported that FODMAPs promote the overgrowth of Gram-negative bacteria in the gut. These bacteria have cell walls that contain lipopolysaccharides, a group of molecules that can inflame the intestinal lining (J. Clin. Invest. 2017, DOI: 10.1172/JCI92390).
Owyang says his group is now starting to identify the specific Gram-negative bacteria that are richest in lipopolysaccharides. "Perhaps we can come up with ways to decrease the growth of those particular bacteria," he says.
Meanwhile, Chey's patients commonly tell him that ingesting various types of food causes their gastrointestinal (GI) problems. "You would think just logically based upon what patients have been telling us for many, many years that there would be many evidence-based diet strategies for patients with GI problems," he says. "Curiously, that has not been the case until probably the last 10 years or so."
Chey says he first learned about the low FODMAP diet in 2008 after reading a paper from Gibson and the rest of the Monash University team (Clin. Gastroenterol. Hepatol. 2008, DOI: 10.1016/j.cgh.2008.02.058). The following year, Chey gave a talk during a postgraduate course for gastroenterologists in the U.S. and asked how many of the gathered doctors had heard of FODMAPs. "Out of an audience of several thousands, fewer than half a dozen hands went up," he recalls. "People had just never even heard of this concept."
He repeated the informal survey at a similar course in 2017. "Probably 80% of the hands went up," he says. And 60% of the doctors said they were using the low FODMAP diet in their clinical practice. In just nine years, he says, the dietary treatment has become wildly popular.