Gut feeling: Is a carbohydrate called fructan giving gluten a bad rap?

Got a stomach ache? Gas? Bloating? You may think, like many others, that your abdominal pain is caused by gluten in the food you’re eating. But research shows gluten might not be the culprit after all.

In a study carried out at the Oslo University Hospital in Norway, 59 people without diagnosed coeliac disease or wheat allergy, but who had self-diagnosed as gluten-sensitive, were tested over several weeks. The subjects ate three different rounds of cereal bars. One round contained gluten, the second fructans, and the third was a placebo with neither. All the bars tasted the same, so the subjects didn’t know which bar they were eating. And they had a week between trials to ensure any symptoms had resolved before moving onto the next type of bar.

The researchers found that the subjects only developed bloating and other symptoms of irritable bowel syndrome (IBS) after eating the bars containing fructan.

Fructans are a kind of short-chain carbohydrate found not just in some grains but also in vegetables such as onions and garlic. They’re poorly absorbed in the small intestine, which causes gastric distress and other IBS symptoms in susceptible people.

Gluten, on the other hand, is a protein complex found in wheat, rye and barley. People with coeliac disease must avoid all gluten because it causes an immune reaction that damages their small intestine.

The finding that fructans, not gluten, is likely responsible for IBS symptoms in people who have not been diagnosed with coeliac or wheat allergy, is not strictly new. Monash gastroenterologist Peter Gibson and nutritionist Jane Muir, who were co-authors on this study, first discovered this in a double-blind cross-over trial in 2013.

Read more: Could people living with coeliac disease one day be able to have their cake and eat it, too?

In that trial, people were exposed to different levels of gluten in foods, as well as a gluten-free control. In the two weeks before the trial, subjects ate a low-FODMAP diet. FODMAP – Fermentable Oligo- Di- Mono-saccharides and Polyols – is an acronym the team coined for the various kinds of IBS-related carbohydrates. To their surprise, in all participants the significant improvement in gastrointestinal symptoms occurred during the low FODMAP run-in period. It was the FODMAPs (including fructans) and not the gluten that were causing their symptoms.

They then took a closer look at the make-up of various grains.

“Our laboratory is set up to test the various FODMAPs in foods. We found that wheat and other gluten-containing grains such as rye and barley also contained high levels of fructans. It appears that fructans and gluten tend to co-exist in foods, and gluten-free grains tend to be low FODMAP,” says Dr Muir.

“So by going gluten-free you are also selecting a lower FODMAP intake. The symptoms improvement you get are due to the reduced FODMAPs – fructan mostly – and not the gluten.”

The current study validates this previous work, and underscores the importance of diet in managing IBS symptoms.

“Often, people who find some relief by avoiding gluten-containing foods still have problems with other foods. Clearly the removal of gluten-containing food is only part of the story, and there are other triggers in their diet. The low FODMAP approach really helps these individuals, as it covers all of these potential triggers of their symptoms.”

So here’s what Dr Muir suggests for people who are experiencing what they think might be a gluten sensitivity. First, she says, it's important to have symptoms checked by a medical doctor to ensure you don’t have coeliac disease or another gastrointestinal disease. You might be diagnosed with irritable bowel syndrome (IBS).

There’s very good evidence that the low FODMAP is a very effective diet therapy for controlling IBS symptoms. The Monash team has developed a smartphone app with an easy guide to which foods are low and high in FODMAPs, as well as recipes and the Low FODMAP Diet Guide.

Finally, it's not necessary to be on a gluten-free diet, says Dr Muir. You can consume bread that contains gluten but is low in FODMAPs. More of these products are becoming available. For example, traditional sourdough spelt breads are very low in FODMAPs. There are also sourdough wheat breads that are low in FODMAPs. The sourdough cultures break down the fructans in the wheat, thereby reducing the level in the final product.

More information the FODMAP diet and the smartphone app