A carb called fructan may be the real culprit behind gluten sensitivity

By Julia Belluz

You can still enjoy sourdough bread on the low-FODMAPs diet.
Photolibrary RM/Getty

Many Americans have become obsessed with avoiding gluten, despite the dearth of scientific evidence proving this protein (found in wheat, rye, and barley) actually makes people who haven’t been diagnosed with celiac disease, a serious autoimmune disease, or wheat allergy sick.

So how to explain the symptoms of people with so-called non-celiac gluten sensitivity — the bloating, stomach pain, and fatigue they say are alleviated with a gluten-free diet?

For the past several years, scientists began to suspect that maybe other elements in grains are causing these digestion issues. And they’ve zeroed in on a group of carbohydrates called FODMAPs, or “fermentable oligosaccharides, disaccharides, monosaccharides, and polyols,” which humans lack the digestive enzymes to break down.

FODMAPs include the fructose in fruits and vegetables, the lactose in dairy products, the galactans in legumes, and the fructans in wheat and rye (as well as in other foods like artichokes, asparagus, leeks, garlic, and onions).

Since fructan is found in many foods that also contain gluten — like pasta and white bread — researchers have had to design studies to try to separate out their effects. A recent study published in the journal Gastroenterology shows that fructan caused more stomach upset than gluten did in a group of people who thought they were gluten-sensitive.

This finding has researchers warning: If you think gluten is upsetting your stomach, it might be fructan instead.

Why researchers started to suspect it’s not gluten making people sick

To understand where this fructan hypothesis came from, let’s step back for a second and go deeper into the science of gluten.

There are definitely real gluten-related disorders that people have to cope with, but these are vanishingly rare. Celiac disease causes people's immune systems to violently attack their small intestine whenever they eat gluten. About 1 percent of Americans have celiac disease, according to the National Foundation for Celiac Awareness. Even more rare are genuine wheat allergies, which affect an estimated 0.1 percent of people in Westernized countries.

As for the other people sensitive to gluten, a recent review of the double-blind, placebo-controlled trials performed so far found that only 16 percent of people who respond to a gluten-free diet had real non-celiac gluten sensitivity. The rest have other food sensitivities or a nocebo response to gluten, meaning they experience symptoms even when they’re not actually eating gluten.

The improvement in symptoms self-reported by gluten avoiders is often "a result of a placebo effect unavoidably related to the elimination diet," Dr. Umberto Volta, a gluten researcher from the University of Bologna in Italy, told me.

And when patients are assessed more thoroughly, Volta added, it's often other factors rather than gluten that cause their gut discomfort.

This observation spurred studies — such as this one, published in Gastroenterology in 2013 — in which researchers examined the effects of FODMAPs. FODMAPs like fructan reach the large intestine undigested, where they’re fermented by bacteria in the gut. That process produces gas and can lead to discomfort for some people — particularly in those with the chronic gut disorder irritable bowel syndrome or just IBS-like symptoms after eating, such as gas, diarrhea, and bloating.

In the 2013 Gastroenterology study, researchers from Monash University in Australia took 37 people who thought they were sensitive to gluten and followed a gluten-free diet. They challenged the study participants to a double-blind crossover trial where participants ate different levels of gluten or, in the control arm, whey protein.

Before they started the study, participants had to follow a low-FODMAP for two weeks.

Monash

“The results were surprising,” said study author Jane Muir, a nutrition researcher at Monash. “In all participants, the significant improvement in gastrointestinal symptoms occurred during the two-week low-FODMAP run-in period.” Meanwhile, whether they ate gluten didn’t seem to have an impact on most of the volunteers.

The researchers then set up a lab to test various FODMAPs in food. “We found that wheat and other gluten-containing grains (like rye, barley, wheat) also contained high levels of fructans,” Muir said in an email. “It appears that fructans and gluten tend to co-exist in foods, and gluten-free grains tend to be low FODMAP.”

So then the researchers decided to zero in on fructans to see if they’re what’s actually causing the symptoms in people with gluten sensitivity — the focus of the new paper.

Why researchers are now blaming fructans for people’s symptoms

For the recent study, published in the journal of Gastroenterology, researchers at the University of Oslo took a group of 59 people who did not have celiac disease but were following a gluten-free diet. Study participants were randomly assigned to eat muesli bars containing gluten, fructans, or a placebo. The bars looked alike and tasted the same, so the study volunteers did not know what they were eating.

After seven days, participants crossed over into a different group, and did so again until they had completed all three bar diets. The participants also tracked their gastrointestinal symptoms — bloating, diarrhea, constipation, pain — throughout.

The fructan bars, it turned out, caused more symptoms than the placebo bars — while the gluten bars had no effect.

“This result strengthens the hypothesis that it is rather the fructans in wheat that is the culprit, not the gluten,” said University of Oslo nutrition researcher Gry Irene Skodje, who led the study, over email.

This research is still in its early stages, and many of the studies involving people with gluten sensitivity or low-FODMAP diets are small. But for those suffering with IBS or IBS-like symptoms, or for people who think they’re gluten-sensitive, the researchers suggest talking to your doctor about a low-FODMAP diet.

In another study, Muir and other researchers found more than 70 percent of IBS patients improved their symptoms by reducing their FODMAP intake — which is why doctors are now prescribing the low-FODMAP diet for some patients.

Switching from a gluten-free to a low-FODMAP diet would mean you’d still have to avoid gluten-containing wheat, rye, and barley — which are also high-FODMAP foods. But you could eat sourdough bread (which is low-FODMAP) or even some types of pasta.

You don’t have to cut out all your FODMAPs. Feeding the bacteria in the gut and producing some gas is not a bad thing. “We now know that the gut microbiome may be very important with wide-ranging effects on our health,” said Muir.

Fructans and other FODMAPs have a “prebiotic effect” on the gut, meaning these carbohydrates stimulate healthy bacteria in the intestines. So if the low-FODMAP diet takes off the way “gluten-free” did, let’s not vilify fructan. Even in those with sensitive stomachs, a little fructan is probably a good thing.