If onions make you feel bloated, you’re not imagining it.
For many people with IBS or sensitive digestion, onions are one of the biggest gut triggers, and it comes down to something called FODMAPs.
What are FODMAPs?
FODMAP stands for:
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Fermentable – broken down by gut bacteria
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Oligosaccharides – in foods like onions, garlic, wheat
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Disaccharides – lactose in dairy products
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Monosaccharides – fructose in certain fruits like apples
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Polyols – sugar alcohols in stone fruit, mushrooms, sweeteners
These carbohydrates are poorly absorbed in the small intestine. When they reach the large intestine, bacteria ferment them, creating gas, bloating, and water retention.
Onions contain a type of oligosaccharide called fructans, which are one of the most poorly tolerated FODMAP groups. Even small amounts can trigger symptoms for some people, especially those with IBS. FODMAP sensitivity is individual. Some people have a higher threshold before symptoms appear, while others react to even small amounts. Factors like gut microbiome diversity, motility, and visceral sensitivity all play a role.
In IBS, nerve endings in the gut wall can be more sensitive to stretching and gas production, which makes fermentation symptoms more noticeable.
The pickling solution
Here’s the good news: pickling onions in an acidic brine, like apple cider vinegar, can help reduce their FODMAP content.
When onions are sliced and soaked, some of the fructans leach out into the liquid. Since fructans are water-soluble, this process can lower their concentration in the onion itself. You still get the flavour, but often with less digestive discomfort.
How to make FODMAP-friendlier pickled onions
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Slice 1 red onion thinly.
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Add to a clean (preferably sterilised) jar with a pinch of salt.
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Combine with a 1:1 ratio of apple cider vinegar (with the mother) and boiling water. Allow to cool slightly
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Pour over the onion in the jar and pickle for at least 1 hour (overnight is ideal for maximum fructan leaching).
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Drain before eating, this step helps remove more FODMAPs. Drain just the portion you are eating, of course.
The gut health bonus
Apple cider vinegar adds organic acids, which can help maintain a healthy gut pH and support beneficial bacteria. While the FODMAP load is reduced, you’ll still benefit from the onion’s antioxidants, like quercetin, and that tangy, crisp bite in your meals.
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