You ate a beautiful pasta, a stir-fry, or a restaurant soup — nothing obviously “unhealthy” — and an hour later your stomach is tight as a drum. The hidden culprit is almost always the same two ingredients: garlic and onion. Here is exactly why they do this, and what actually fixes it.
Why garlic and onion cause bloating
Garlic and onion are among the most concentrated natural sources of fructans — chains of fructose molecules that plants use to store energy. Fructans belong to the FODMAP family of fermentable carbohydrates, and they share one defining feature: the human small intestine has no enzyme capable of breaking the fructose-fructose bonds that hold them together.
Because they cannot be digested or absorbed, fructans travel intact all the way to your large intestine. Two things then happen at once. First, the fructans act as osmotic agents, drawing water into the bowel. Second, the trillions of bacteria in your colon treat the fructans as a feast and ferment them rapidly, producing hydrogen, carbon dioxide and methane. Water plus gas equals distension — the visible, painful bloating you feel after dinner.
What makes garlic and onion so sneaky is that they are everywhere: stocks, sauces, dressings, spice blends, marinades and “natural flavoring”. You can avoid the obvious clove and still get a meaningful fructan dose from a restaurant sauce.
Who is most affected
Everyone produces gas from fructans — it is normal physiology. The difference is who feels it. People with IBS have visceral hypersensitivity, meaning their gut nerves register normal amounts of stretch as pain and bloating. So the same fermentation that a friend never notices can leave you doubled over.
There is also a large group of people with non-celiac wheat sensitivity who blame gluten. Because wheat, garlic and onion all contain fructans, removing wheat accidentally lowers the fructan load and symptoms ease — reinforcing the wrong conclusion. Studies suggest many self-described gluten-sensitive people are in fact reacting to fructans, not the gluten protein. If that sounds like you, our deep dive on how fructan hydrolase resolves wheat and onion sensitivity is worth a read.
The low-FODMAP diet approach (and its limits)
The standard first-line strategy is the low-FODMAP diet, which temporarily removes high-FODMAP foods and then reintroduces them to pinpoint triggers. It works — about three in four people with IBS improve. For garlic and onion specifically, the usual workarounds are:
- Garlic-infused oil. Fructans are water-soluble, not oil-soluble, so the flavor transfers but the fructans do not.
- The green tops of scallions and leeks, which are low in fructans, instead of the bulb.
- Asafoetida (hing), a pinch of which mimics the savory note in small amounts.
These tricks help, but they come at a cost: complexity, constant vigilance, and a social tax. Strict long-term restriction can also reduce the beneficial fibers that feed a healthy microbiome, and it makes eating at restaurants or a friend’s house genuinely stressful. The low-FODMAP diet is a brilliant diagnostic tool — but as a permanent way of life, it is a heavy lift.
How digestive enzymes solve this
If the problem is a missing enzyme, the most direct solution is to supply that enzyme. This is the same logic behind the lactase pills lactose-intolerant people take with dairy — extended to fructans. Taken with the first bite of a garlic- or onion-containing meal, a fructan-targeting enzyme breaks the fructan chains down into simple, absorbable sugars in the small intestine, before they can reach the colon to ferment. No fermentation, no excess gas and water, no bloating.
Enzymes are not a replacement for identifying your triggers, and they cannot cover polyols (sorbitol, mannitol). But for the specific, maddening problem of garlic and onion, they turn an unavoidable trigger into an occasional, manageable one. For the bigger picture across all four FODMAP groups, see our guide to digestive enzymes for IBS.
Eat garlic again.
Fodyzen's fructan hydrolase breaks down the fructans in garlic, onion and wheat before they can ferment — alongside three more enzymes for complete FODMAP coverage.
Eat Garlic Again — Try Fodyzen® →Fodyzen fructan hydrolase, explained
Fructan hydrolase is the hard-to-formulate enzyme at the center of Fodyzen. It is engineered to cleave the beta-2,1 and beta-2,6 fructose bonds that define fructans — the exact bonds the human gut cannot touch. In a 2026 in-vitro intestinal model, it broke down 90% of fructans within 30 minutes, and in the accompanying randomized, placebo-controlled trial of 124 adults with IBS, 78% reported less bloating after four weeks (Kaye et al., Gastro Hep Advances, 2026).
Crucially, Fodyzen does not stop at fructans. It pairs fructan hydrolase with lactase, alpha-galactosidase and xylose isomerase, so a single capsule or sachet covers dairy, beans, wheat, onion and high-fructose fruit in one go. If garlic and onion have been quietly running your life, that is the combination worth knowing about — start with the complete guide to FODMAP digestive enzymes.
Frequently asked questions
Why do I bloat after eating garlic and onion?
Garlic and onion are exceptionally high in fructans — a FODMAP carbohydrate humans cannot digest. The undigested fructans travel to the colon, where bacteria ferment them into gas and pull water into the bowel, causing bloating, wind and cramping, especially in people with IBS.
Is garlic and onion bloating the same as a gluten problem?
Usually not. Wheat, garlic and onion all contain fructans, so people often blame gluten when the real trigger is the fructan. Many who think they are gluten-sensitive are actually fructan-sensitive, which is why removing wheat seems to help.
Does garlic-infused oil cause bloating?
Typically no. Fructans are water-soluble, not oil-soluble, so the flavor infuses into oil but the fructans do not. Garlic-infused oil is a common low-FODMAP way to keep the flavor without the symptoms.
How can I eat garlic and onion without bloating?
Options include garlic-infused oil, the green tops of scallions, and strict portion control. For the real thing, a fructan-targeting enzyme such as fructan hydrolase — taken with the first bite — breaks the fructans down before they can ferment.
Maya Reyes is a registered dietitian specializing in functional GI disorders and the low-FODMAP diet. She leads clinical formulation and research at Fodyzen.