onion
Vegetables
Trigger checker for onion
See onion rated across every trigger — FODMAP, histamine, salicylate, oxalate, tyramine and more — plus diet compatibility, all in one quick ingredient profile.
Related checkers
Compare onion across criteria
Triggers
Diets
Serving size, prep, and portion notes for onion
Onion is graded E for fructans and E for total FODMAPs, the top of our scale, which is why it is the single most common trigger people uncover once they start logging food against symptoms. The reaction is a carbohydrate problem rather than an allergy: onion is A for histamine, A for oxalates, A for lectins and A for nightshades, so if onion bloats you the fructans are almost certainly the mechanism. It also grades E for low fermentation SIBO plans. The frustrating part is that fructans are water soluble and heat stable, so caramelizing, slow simmering or fishing the pieces out of a sauce does not make onion any safer, and onion hidden in stock, gravy and spice blends is why so many people react to restaurant food they cannot account for.
Watch for
Fructans and total FODMAPs both graded E, the highest tier we use, and the grade does not soften between raw and cooked onion / Cooking is not a fix: fructans dissolve out of the onion into the pan and stay in the liquid, so straining the pieces out leaves the trigger in the sauce / Hidden onion drives most unexplained flare-ups: stock cubes, gravies, curry pastes, spice rubs, chips and anything listed as seasoning or natural flavor / Graded E for low fermentation SIBO, so onion is usually one of the first things pulled when working through a SIBO protocol / Clean on the rest of the chemistry (histamine A, oxalate A, lectin A, nightshade A, with only a borderline B for histamine liberation), which is why an onion reaction is nearly always intolerance rather than allergy
Explore related in Vegetables
Compare similar foods to build a personalized list of swaps that work for your system.
FAQ
What does the FODMAP rating mean for onion?
High FODMAP: consider smaller servings or swap within the same group.
Is onion generally well tolerated?
FODMAPs (Avoid) and Fructans (Avoid) Start with those if you react.
What should I check next?
Compare within the Vegetables group.