Is Onion Low FODMAP? A Complete Guide to Onions and Substitutes

Michael Eisenwasser 7 min read

Onion is in almost every savory recipe. Soups, stews, stir-fries, chili, meatballs, burgers, salsa, sauces, dressings. The minute you start the low-FODMAP diet, onion is one of the first things off the menu, and the obvious question is: what replaces it?

This post covers exactly which onions and onion-adjacent ingredients are high FODMAP, which parts are safe, and the specific swaps that actually work. If you've already read our garlic post, a lot of this will feel familiar. Garlic and onion are siblings in the fructan family, and the rules track closely.

The short answer

Standard onions (yellow, white, red, brown, Spanish, Vidalia, sweet) are high FODMAP at typical serving sizes, and they're avoided during the elimination phase of the low-FODMAP diet.

Green tops of scallions (spring onions), chives, and leek greens are low FODMAP and give you the oniony flavor you're missing.

Why onion is high FODMAP

The "O" in FODMAP stands for oligosaccharides, which includes fructans. Onions are one of the most concentrated fructan sources in the Western diet, alongside garlic and wheat.

Fructans are chains of fructose molecules. The human small intestine can't break them down, so they travel intact to the large intestine, where bacteria ferment them. That fermentation produces gas and pulls water into the gut. In people with IBS, that's what triggers bloating, cramping, urgency, and altered bowel habits. Shepherd and colleagues showed this directly in a placebo-controlled trial back in 2008, and subsequent research has continued to support fructans as a major dietary trigger in IBS.

Onion is such a consistent trigger that many IBS patients figure it out on their own, years before they ever hear the word FODMAP.

All the onions that are high FODMAP

This is the list Monash flags as high-FODMAP or "avoid during elimination":

• Yellow, white, red, brown, Spanish, sweet, and Vidalia onions. All high FODMAP.
• Shallots. A single small shallot is high in fructans. Don't treat them as a "milder" swap, they're not.
• Pearl onions and cocktail onions. Same plant, same fructans, smaller size. Still high FODMAP.
• The white bulb of a scallion (spring onion). High fructans. Only the greens are safe.
• The white bulb of a leek. High FODMAP. Only the dark green tops are safe.
• Pickled onions. Pickling doesn't remove fructans.
• Caramelized onions. Cooking concentrates the flavor but doesn't destroy fructans.

If a recipe calls for "onion" without specifying, assume it means the high-FODMAP kind.

Onion powder, onion salt, and dehydrated onion

This trips people up constantly. Drying an onion removes water, not fructans. If anything, dried onion is worse than fresh, because the fructans get concentrated into a smaller volume.

• Onion powder. High FODMAP at standard cooking amounts. A teaspoon of onion powder packs more fructans than you'd get from a similarly sized piece of fresh onion.
• Onion salt. Same problem. It's onion powder with salt added.
• Dehydrated onion flakes. Same concentrated fructans. Skip during elimination.
• "Onion extract" or "onion flavor" on a label. A common hidden source of onion fructans in processed foods. If the product isn't Monash or FODMAP Friendly certified, it's safer to skip during elimination and confirm later during reintroduction.

The exception worth knowing: a few brands now sell low-FODMAP certified onion-flavor products, like Gourmend's green onion powder. Those are lab-tested and safe at the serving size on the label. Regular supermarket onion powder is not.

Hidden onion in processed food

This is where people get blindsided. Onion is in way more packaged food than most cooks realize.

Common culprits:

• Stocks, broths, and bouillon cubes. Almost all commercial stock (chicken, beef, vegetable) is made with onion. Even "low sodium" and "organic" versions. You need to check the label every time.
• Pasta sauces and pizza sauces. Onion is in the base of nearly every jarred sauce.
• Salad dressings. Ranch, Caesar, Italian, French. Almost all contain onion or onion powder.
• Seasoning blends. Taco seasoning, chili powder blends, poultry seasoning, "Italian herbs," barbecue rubs. Read the ingredient list on each one.
• Chips and savory snacks. Sour cream and onion, barbecue, ranch, salt and vinegar. Onion powder is everywhere.
• Gluten-free products. Gluten-free bread, pies, and crackers often use onion powder for flavor since they can't rely on wheat.
• "Natural flavors" or "spices." On a savory product, this frequently includes onion or garlic. If you can't confirm, treat as high FODMAP during elimination.

A key food-science point: fructans are water-soluble. When onion cooks in broth or sauce, the fructans leach into the liquid. So the trick of "just pick out the onion pieces before serving" doesn't work for anything water-based. The liquid itself is now high FODMAP.

This is different from oil. Fructans are not fat-soluble, which is why onion-infused or garlic-infused oils work as flavor carriers. We covered the mechanism in detail in the garlic post.

What's actually safe: low-FODMAP onion swaps

The good news is there are several real options, and layered together they get you most of the way back to normal cooking.

Green scallion tops (spring onion greens). The dark green part of a scallion is low FODMAP at generous serving sizes, well beyond what most recipes call for. Slice thin and add near the end of cooking so they keep their bite. Check the current Monash app for the exact gram threshold in your region.

Chives. Low FODMAP at standard serves. Great for garnish, eggs, baked potatoes, dips, and cream cheese spreads. Use fresh if you can. Freeze-dried chives work too.

Garlic chives (Chinese chives). A different plant with a more garlicky note. Low FODMAP in normal cooking serves. Good in stir-fries, dumplings, and scrambled eggs.

Leek greens. Only the dark green tops, not the white or pale-green bulb. Low FODMAP at standard cooking serves. Slice and cook them like you would onion. They soften nicely and add sweetness to soups and braises.

Asafoetida (hing). A sulfurous resin used in Indian cooking. When a pinch hits hot oil, it tastes remarkably like cooked onion and garlic together. Buy pure asafoetida. Some commercial hing is cut with wheat flour, which adds fructans back in.

Infused oils. Onion-infused and garlic-infused oils carry the flavor without the fructans. Buy a Monash-certified brand, or make your own by warming oil with onion chunks, straining out every solid, and refrigerating.

Certified low-FODMAP onion powders. Products like Gourmend green onion powder and FODY-branded seasonings use the green parts and are tested for safe serving sizes.

FODMAP stacking with onion substitutes

One quick caution. Each of these substitutes is low FODMAP on its own at the listed serving, but they do still contain small amounts of FODMAPs. If you pile chives, scallion greens, and leek greens into the same dish in large quantities, you can stack your way over threshold. That's true of any low-FODMAP ingredient. The dose is what makes it safe, and portions add up across a meal.

Tracking what you eat and how your gut responds is the fastest way to see these patterns. That's the whole reason we're building FODMAP Tracker.

Building a weeknight dinner without onion

A pattern that works well: start with olive oil and a spoonful of garlic-infused oil in the pan. Add the green tops of a couple of scallions. Add your protein. Season with salt, pepper, and a Monash-certified spice blend. Finish with chives or more scallion greens. Serve over rice or gluten-free pasta.

It's not a compromise dish. It tastes like normal cooking, because it is. The goal of the elimination phase isn't to suffer through it, it's to reset your gut so you can figure out what actually triggers you during reintroduction.

For more meals that use this pattern, see our low-FODMAP recipes.

When can you eat onion again?

Elimination isn't forever. The typical window is 2 to 6 weeks, then you move into reintroduction, where you test each FODMAP group to find your personal tolerance. Fructans, the group onion belongs to, is one of the standard reintroduction challenges.

Most people don't get back to "unlimited raw onion" levels, but a fair number tolerate small cooked amounts once they've reset. You won't know your number until you test it. Until then, green tops and infused oils carry the flavor.

Track your symptoms and discover patterns with FODMAP Tracker. Includes a database of 1,000+ foods with FODMAP ratings.