It Was Probably the Fructans, Not the Gluten
Why gluten-free diets help IBS sufferers — and why the reason isn't what most people think.
A lot of people with IBS try going gluten-free and feel noticeably better. Then they conclude they're gluten-sensitive. It's a reasonable conclusion — but it's probably wrong.
In 2017, researchers at Monash University ran a double-blind crossover trial on 59 people who believed they had non-coeliac gluten sensitivity. Each participant cycled through three diets: high gluten, low gluten, and low fructan. The result was clear. Fructans — not gluten — triggered significantly more bloating, gut pain and wind. On the low-fructan diet, symptoms dropped substantially. On the gluten variations, not so much.
Why gluten-free still works
Most foods that contain gluten also contain fructans. Wheat, rye, barley — they're all high-fructan grains. When you remove gluten from your diet, you're also removing fructans. Symptoms improve, and gluten gets the credit.
This matters practically because gluten-free and low-fructan are not the same thing. Gluten-free products often contain:
- —Apple or pear juice (high fructose)
- —Honey (high fructose)
- —Inulin — a fructan added as a prebiotic fibre for texture and gut health marketing
- —Chicory root extract — another fructan source
A gluten-free bread made with inulin can trigger IBS symptoms as reliably as regular bread. The label says gluten-free. The FODMAP content says otherwise.
The sourdough exception
Traditional sourdough is often tolerated by IBS sufferers even though it's made from wheat. The long fermentation process — 8–12 hours with a live culture — allows bacteria in the dough to break down most of the fructans before the bread reaches you. By the time it's baked, the fructan content is substantially lower.
This only applies to genuine sourdough — bread made with a starter culture and long fermentation. Most supermarket "sourdough" is regular bread with a small amount of vinegar added for flavour. Check that the ingredients list only flour, water, salt, and starter culture.
What this means for testing
If you've never done a proper FODMAP elimination and reintroduction, you don't actually know whether gluten is a problem for you. (If you have coeliac disease, that's a different situation — coeliac is an immune response to gluten itself and requires strict avoidance regardless.) For everyone else, the fructan reintroduction test — not the gluten one — is the relevant experiment.
The practical upside: if fructans rather than gluten are the issue, your dietary restrictions are different and often more manageable. Gluten-free means avoiding a protein found in many grains. Low-fructan means watching specific foods — but at the right serving sizes, many gluten-containing foods (sourdough, small amounts of pasta) may still be on the table.