Garlic intolerance symptoms: why garlic and onion bloat you, and how to test it

Garlic intolerance symptoms live in your gut: bloating, gas, belly pain and loose poop, usually a few hours after the meal. Onion intolerance feels the same, for the same reason. Both are full of fructans, a plant fiber your body can't digest, so your gut bacteria ferment it and make gas. To find out if garlic or onion is your problem, cut both for two weeks, then bring them back in steps.

Garlic and onion intolerance symptoms show up hours after the meal

You have garlic pasta at lunch, and by mid-afternoon your waistband feels a size smaller. That's the classic pattern. The most common signs:

• bloating, the tight, inflated feeling, often worse as the day goes on
• gas, and more of it than usual
• cramps or a dull belly ache
• loose or urgent poop, sometimes the next morning

The delay is the confusing part. Your gut takes its time with garlic and sends the bill later, so the meal you blame is often the wrong one. In a scanner study of 16 healthy volunteers, a fructan drink filled the colon (the large intestine, the last stretch of your gut) with gas that was easy to see about four hours later (Murray et al. 2014). If dinner was onion soup and the bloating hits at bedtime, the soup is a fair suspect.

Fructans are why garlic and onion make you bloated

Fructans are chains of sugar that your small intestine has no tool to break down. They pass through untouched and reach your colon, where your gut bacteria eat them and make gas as they go. Fructans are one of the FODMAPs, a type of carb that ferments in your gut and can cause gas.

Garlic and onion are loaded with them. When researchers measured fructans in 60 vegetables, the top five were garlic, artichoke, shallots, leek bulb and onions (Muir et al. 2007).

Everybody's bacteria ferment fructans. In that scanner study, the fructan drink clearly added gas to the volunteers' colons, and they barely felt it (Murray et al. 2014). Some guts just seem to mind the stretch more.

A blinded test involved 25 people whose gut symptoms had eased on a diet low in fructans and fructose, the sugar found in fruit. They drank test drinks with meals without knowing what was in them. When the drink held fructans, 77% said their symptoms weren't under control. When it held glucose (a plain sugar your body absorbs easily), 14% did. Bigger doses brought stronger symptoms (Shepherd et al. 2008). So a sprinkle of onion powder and a whole fried onion are two very different tests.

What a food test can show

A food test records how your bloating changes when you change garlic or onion. Immune reactions to garlic have also been reported (Hellu et al. 2023).

Is it normal to only react to garlic and onion?

It's a common pattern. Garlic and onion top the fructan list among vegetables, and they turn up in a lot of savory food, so they get noticed first. If big servings of leeks, shallots or artichokes also leave you bloated, fructans are probably the common thread. A test will tell.

How to test for garlic intolerance in 2 weeks

A food diary can give you a hunch. Changing one thing and watching what your body does gives you an answer. The plan below tests garlic and onion together first, because they hide in the same foods.

Weeks 1 and 2: cut garlic and onion, hidden ones included

The obvious cloves and rings are easy. The hidden ones catch people out.

Read labels for "onion powder", "garlic powder" and "dehydrated onion". Keep the rest of your eating as normal as you can, so garlic and onion are the only things that change. Log how your gut feels and your poop every day.

Week 3: bring them back in steps

Bring one food back at a time. Start with garlic, for example.

Then do the same with onion, from a spoonful up to a normal portion. Stop increasing the portion if your symptoms come back. Note how much you ate.

You may well get your garlic back. When people using a low-FODMAP diet app brought foods back one at a time, onion was flagged as a trigger in 39% of tries and garlic in 35% (Dimidi et al. 2023). In the other tries, no trigger showed up, and the food could stay on the menu.

How to read your result

An IgG food test can't spot a garlic intolerance

Home kits sold as intolerance tests measure IgG, a protein your body's defense system makes when it encounters a food. A European allergy task force advises against IgG4 food testing for intolerances. IgG4 to a food mostly shows you've been eating that food (Stapel et al. 2008). Your own two weeks can show whether your bloating changes.

Run the test in Gut Twin

In Gut Twin, you pick meals from a food list, log how your gut feels and your poop, and run one small test at a time against your own days, like two weeks without garlic and onion. Each test ends as helped, no change, worse or unclear. Until the test finishes, garlic and onion stay suspects.

What we don't know yet

The studies on fructans used drinks and powders with a measured dose, so nobody can say how many cloves are too many for you. Most of them looked at people with sensitive guts. Why some guts mind fructan gas more than others is still being worked out. We found no study that follows people over years, so whether you can develop an onion intolerance later in life is still an open question. A home test may still leave the answer unclear.