Why Do Onion & Garlic Trigger My IBS Symptoms?

Garlic and onion are both incredible, antioxidant-rich vegetables that are used as the foundation of most dishes. Their flavor profile reaches across cultures, and is found in some form in most kitchens around the world. But why do they cause issues for those with IBS?


Garlic and onion are both rich in an oligosaccharide (carbohydrate molecule) called fructan. The body is unable to fully break down these molecules in the small intestine, and only absorbs about 5-15% of fructan molecules we eat. This means that our beneficial bacteria in the gut can feed on the remaining molecules. As a result, they produce gas that can be painful in those with IBS. This could be due to fewer beneficial bacteria in the gut or fewer enzymes present that can break these molecules down. Undigested fructan molecules can also pull water into the gut as they move through the intestines, which leads to bloating and diarrhea.

This is true of all FODMAP molecules, so why does garlic and onion seem like more intense triggers? Garlic and onion are both highly concentrated in fructans, so they may be more potent as triggers if you are sensitive to fructans.

Does that mean you can never enjoy the flavor of garlic or onion again? Absolutely not!

There’s a chance that you may be able to tolerate small portions of garlic and onion. If you’ve never challenged them, do it! You may be able to enjoy them without the stress of symptoms. If you are challenging them, try them cooked versus raw, as they may be better tolerated this way. If you find that they are major trigger foods for you, you still don’t have to miss out on their flavor. Garlic and onion are both water soluble, so it may not be possible to just eat around them. But, it is possible to infuse their flavors into oils. You can do it yourself or buy it from a company that did it for you!

Source: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3934501/