If you're someone with a sensitive tummy and you've never heard of FODMAPs, listen up. In addition to fructan in wheat (and garlic and artichokes), FODMAPs include fructose (found in some fruit), lactose (found in some dairy products) and galactans (found in some legumes).

While most people can digest FODMAPs no problem, for many with chronic gut disorders like irritable bowel syndrome, they're poorly absorbed by the small intestine and then fermented by bacteria to produce gas, which leads to those unpleasant symptoms. IBS affects up to 20 percent of Americans.

After a team of scientists at Monash University in Australia lead by Peter Gibson and Susan Shepherd linked FODMAPs to IBS in 1999, they designed the low FODMAP diet. According to William Chey, a gastroenterology and professor of medicine at the University of Michigan, the diet has been swiftly embraced by doctors and dieticians as a treatment for IBS that's as effective as the drugs on the market. (In most trials, 70 percent of patients see improvement in their IBS symptoms when they go on the low FODMAP diet.)

Yet the gluten-free diet is still way more popular and well-known than the low FODMAP diet. And that's led researchers to want to try and separate the effects of the gluten protein from the FODMAPs in foods like wheat where they're both found.

Back around 2010, Jessica Biesiekierski, who's now a post-doctoral research fellow at the Translational Research Center for Gastrointestinal Disorders in Belgium, heard that a lot of people with IBS in Melbourne, Australia were claiming to experience benefits from the gluten-free diet. That gave her the idea to do a trial to test gluten sensitivity in these people who didn't have celiac disease while she was a grad student at Monash.

In a study published in 2011, Biesiekierski and a team of researchers at Monash (who were also involved with the FODMAP research) showed evidence of the existence of non-celiac gluten sensitivity in a randomized controlled trial of 34 people, some of whom got gluten and some of whom got placebo.

"Everybody was jumping up and down since that was the first study to show gluten could induce symptoms in patients that did not have celiac disease," Biesiekierski tells The Salt. It also helped fuel the explosion of gluten-free food: The number of people with celiac disease is small — less than one percent of the population — but suddenly it seemed possible that a lot more people were sensitive to gluten and should avoid it.

Given the response to the study, the team decided to try to reproduce their results. This time, 37 subjects with non-celiac gluten sensitivity and IBS were randomly assigned to groups given a two-week diet of reduced FODMAPs, and were then placed on high-gluten, low-gluten or control diets for one week.

The results, published in 2013 in the journal Gastroenterology, were intriguing. Only 8 percent of the participants had gluten-specific effects from the gluten diets, while all participants has significantly improved symptoms on the low FODMAP diet. The researchers concluded that gluten had no specific or dose-dependent effects on patients who claimed to be gluten sensitive but were not diagnosed with celiac disase.

"We believe non-celiac gluten sensitivity probably does exist, but it's not very common and we have a lot more to do until we fully understand [gluten]," Biesiekierski says.

And, Biesiekierski says, for the majority of the people with IBS, FODMAPs like fructan are more likely to be the trigger than gluten. "That means we really have to understand the differences between gluten sources and FODMAP sources," she says, to help people figure out what's upsetting their tummies and how to avoid the triggers.

What's more, in a survey published in April, Biesiekierski found that some people who put themselves on gluten-free diet still had some symptoms, which suggests they could be sensitive to FODMAPs other than the ones in wheat.

Chey, the gastroenterologist at the University of Michigan, agrees that fructans in wheat are more likely to be triggering IBS in most patients than the gluten. "But we still need to understand which symptoms are related to gluten, and [which] ones related to fructans," he says.

And it's exceedingly difficult for scientists to answer these questions.

"It's really hard to design and execute studies that really separate out constituent effects of food," says Chey. "We've still got a long ways to go."

Regardless, Chey says, "a number of people, including me, now feel that non-celiac gluten sensitivity is a misnomer. We should be saying wheat intolerance."

Another critical determinant of gut health scientists are scrambling to understand is the community of microbes in the digestive tract, as we've reported. Chey notes that what you eat influences your microbiome and your microbiome influences how your ferment carbs like FODMAPs that reach your colon.

While many people claim to feel better when they cut out the gluten, there's also a question as to how many of them are experiencing the nocebo effect — when believing that something makes you sick causes it to do so.

Despite the confusion — or perhaps because of it — gluten-free food is spreading through the market like wildfire. According to Mintel, a market research company, sales of gluten-free products reached about $10.5 billion in 2013. And the company expects them to rise to $15 billion annually by 2016. The gluten-free diet isn't just trendy in the U.S. It's also taking off in Europe and Australia.

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