Fructans: The Hidden FODMAP in Wheat, Onion, and Garlic

FODMAP

By the Ration Editorial Team · Reviewed against primary research · Updated July 25, 2026

Track your food and see where fructan load adds up. Track it free with Ration →

Key takeaways

Fructans are chains of fructose that humans lack the enzyme to break down, so they ferment in the colon.
Wheat, onion, and garlic are the biggest dietary sources — which makes fructans hard to avoid.
In IBS they are a leading symptom trigger, and evidence suggests they, not gluten, explain many wheat reactions.

What fructans are

Fructans are short chains of fructose units with a glucose cap. Humans do not produce the enzyme to break the fructose-fructose bonds, so — unlike most carbohydrates — essentially everyone passes fructans undigested to the colon, where gut bacteria ferment them.^[1] In most people that is harmless and even prebiotic. In sensitive guts it is a problem.

Why you might want to limit them

Fructans are one of the FODMAPs, and in irritable bowel syndrome they are among the most common triggers of bloating, gas, and pain.^[3] There is a twist worth knowing: in people who report "gluten sensitivity" without celiac disease, a randomized crossover trial found that fructans — not gluten — provoked the gut symptoms, since wheat carries both.^[2] So some apparent gluten reactions are really fructan reactions. For anyone without IBS or that sensitivity, fructans are beneficial fiber, not something to cut.

Foods highest in fructans

Wheat and rye — bread, pasta, couscous (large amounts because of how much is eaten)
Onion, garlic, leek, and shallot
Artichoke, asparagus, and chicory root (inulin)
Some legumes and dried fruit

How to cut it

The low-FODMAP approach is the evidence-based route: restrict high-fructan foods for a few weeks, then reintroduce to find your tolerance rather than avoiding forever. Practical tricks: garlic-infused oil delivers the flavor without the (water-soluble) fructans; the green tops of scallions and leeks are lower than the bulbs; and sourdough fermentation lowers wheat fructans. Do this with a dietitian where you can — over-restriction has its own costs.

Bottom line

Fructans are a top IBS trigger and the likely culprit behind many "gluten" reactions. If your gut is sensitive, use a structured low-FODMAP reintroduction to find your limit; if it is not, they are healthy fiber. Research summary, not medical advice.