Short answer: No, onion is NOT low FODMAP. All varieties of bulb onion — white, yellow, red, brown, spring onion bulbs, shallots — are high in fructans even in tiny 1-tablespoon amounts. According to the Monash University FODMAP Program, onion is one of the most common IBS triggers.
The good news? You can absolutely get that savory onion flavor safely — with green onion tops, chives, asafoetida, and garlic-infused oil.
Onion FODMAP Content at a Glance
| Onion Type | Low FODMAP Serving | Verdict |
|---|---|---|
| White / brown / yellow onion (bulb) | None — high fructans even at 1 tsp | 🔴 Avoid |
| Red onion | None | 🔴 Avoid |
| Shallots | None | 🔴 Avoid |
| Pickled onions | None | 🔴 Avoid |
| Spring onion — white bulb | Avoid | 🔴 Avoid |
| Spring onion — green tops only | Unlimited | 🟢 Safe |
| Leek — green tops only | 2/3 cup (54g) | 🟢 Safe |
| Chives | 1 tbsp | 🟢 Safe |
| Asafoetida (hing) | 1/8 tsp | 🟢 Safe |
Why is onion so bad for IBS? Onion contains fructo-oligosaccharides (fructans) that humans can't digest. In the large intestine they ferment rapidly, causing bloating and cramping within 30–90 minutes.
Are Cooked Onions Low FODMAP?
No. Cooking does not destroy fructans. Sautéing, roasting, or boiling all keep onions high FODMAP. Fructans are water-soluble, so even straining onions out of broth doesn't help.
The 5 Best Onion Swaps
- Green onion tops — the closest match.
- Chives — great in eggs, dips, potatoes.
- Garlic-infused olive oil — fructans don't dissolve in oil.
- Asafoetida (hing) — mimics onion + garlic.
- Leek leaves (green only) — sweet and mild.
Find more with our Ingredient Swap Finder or check foods with the FODMAP Food Checker.
Hidden Onion in Packaged Foods
Watch for onion powder, dried onion, "natural flavors," vegetable stock, gravies, salad dressings, sausages, and tomato pasta sauce.
Onion During Reintroduction
After elimination (2–6 weeks), reintroduce fructans systematically. Start with 1/4 small cooked onion, wait 3 days, track symptoms with our Symptom Tracker. See our full FODMAP guides.
FAQ
Can I use onion stock cubes? Only Monash-certified brands (FODY, Massel 7s).
Is caramelized onion low FODMAP? No — it concentrates fructans further.
Pickled onions? Still high FODMAP.
The Bottom Line
Onion in every form (except green tops and chives) is a strict avoid during elimination. Stock up on garlic-infused oil, scallion greens, and chives. Browse low FODMAP recipes — every one is onion-free.
Reviewed against Monash University FODMAP research and NIDDK IBS guidelines. Informational only, not medical advice.