Can I eat onions with ulcerative colitis?
Onions are particularly rich in fructans, a fermentable oligosaccharide FODMAP that Monash FODMAP research and Cleveland Clinic both identify as a common bloating and gas trigger. Fructans are water-soluble, so they leach into broths and sauces even if the onion pieces are removed before eating, and raw onion is also commonly reported as a direct gut irritant.
During a flare
Raw onion is commonly avoided during a flare; cooked onion still carries fructans that dissolved into the dish, so it can still trigger symptoms even after straining out the pieces.
In remission
Tolerance is very individual and dose-dependent; some people manage small cooked amounts, others need to limit or avoid onion long-term.
Ways to make it gentler
- use the green tops of scallions or chives instead of the bulb
- try onion-infused oil, since the fructans don't dissolve into fat
Safer swaps
scallion/spring onion greens · chives · onion-infused oil
Sources
- FODMAP food list — Monash FODMAP
- All about onion, garlic and infused oils on the Low FODMAP Diet — Monash FODMAP
- Low-FODMAP Diet: What It Is, Uses & How To Follow — Cleveland Clinic
Last checked 2026-08-12
