Do you love onions but suspect that onions may not love you back? If you’ve ever noticed an uptick in symptoms of smelly gas, belly bloat, and/or diarrhea after eating onions, this sounds like an onion intolerance– and yes, in case you’re wondering– that’s a real thing!
Onions are actually a surprisingly common symptom trigger for many people with digestive disorders of all kinds. The good news is there are certain cases in which you can safely incorporate IBS-friendly variations (or quantities) of onions into your diet. But first, there are certain things you must consider (but most people, even practitioners, miss).
Read on to learn how to navigate onions and irritable bowel syndrome (IBS) from a holistic nutrition standpoint.
Disclaimer: This post was written for general educational purposes only, not to replace 1-1 dietary and medical consultation from qualified healthcare providers.
Table of Contents
3 Ways Onions May Trigger IBS Symptoms
If onions are a food-symptom trigger, you may experience any or all of the following IBS symptoms after eating onions:
- Gas
- Bloating (abdominal distention)
- Diarrhea
- Abdominal pain/cramping
- Constipation
However, the underlying reason and root-cause behind your onion intolerance symptoms may be different from others who experience similar symptoms after eating onions.
Fructans
Whether fresh or cooked, most types of onions are naturally high in fructans– a type of oligosaccharide (the “O” in FODMAP).
- FODMAP is an acronym for “fermentable oligosaccharides, disaccharides, monosaccharides, and polyols” and refers to the different types small, poorly digested carbohydrates that are most likely to be fermented by microbes (bacteria or fungal overgrowth) in our intestines.
According to Monash University (the leading authority on all things FODMAPs), more than one standard sized ring of a red onion, one small ring of a white onion, or more than tablespoons of fresh diced Vidalia onions is high in fructans.
So, if fructans are the reason for your onion intolerance, you may notice that you experience similar symptoms after eating garlic, whole wheat pasta, cashews, pistachios, or other high-fructan foods due to a subsequent fructan intolerance.
Sulfur
On the other hand, not everyone who feels sick after eating onions and garlic is feeling that way because of a fructan intolerance. Another thing that onions and garlic share in common is their high sulfur content.
Sulfur is an essential mineral naturally abundant in most types of meat as well as eggs, cruciferous veggies (think: broccoli, cauliflower, brussel sprouts, etc.), certain antioxidants (like glutathione, alpha-lipoic acid, N-acetyl cysteine) as well as garlic, and– you guessed it– onions.
If a sulfur intolerance is the culprit of your adverse reaction to onions, in addition to reacting to those high-sulfur foods, you may also be experiencing strange symptoms such as:
- Sulfur-smelling gas (resembling the distinct smell of rotten eggs)
- Pins and needles in your hands and feet, fingers and toes
- Body pain
- Feeling “toxic”
A sulfur intolerance is often (but not always) caused by overgrowth of certain sulfur-reducing microbes in your gut, and may even be caused by hydrogen sulfide SIBO.
On the other hand, some people experience sulfur intolerance secondary to mold illness (which creates a molybdenum deficiency in your body), or certain gene variants that block cellular pathways impacting your body’s natural ability to break down sulfur.
(I’ll be sharing more tips on how to uncover and overcome a sulfur intolerance in future content!)
Fiber (roughage)
To be clear, fiber isn’t inherently bad. In fact, fiber is generally beneficial and necessary for a healthy gut! But if your gut is inflamed, foods high in fiber (like raw onions of any kind) may be too tough on the tissue of your gut barrier.
In these cases, you may notice a similar reaction when eating other raw veggies, even those that are low in FODMAP (salads, raw carrots, etc.). I’ve also observed in clinical practice that many people with SIBO often find that fiber makes their symptoms worse.
You may want to bring up the possibility of a fiber intolerance with your healthcare team if you find that raw onions, or onions consumed alongside other high-fiber, raw foods, make your IBS symptoms worse.
Recommended reading: Fiber: Friend or Foe?
Dietitian-Approved Ways to Try Onions with IBS
Enzyme replacement
While not everyone with IBS or SIBO has a fructan intolerance, it’s pretty common and can be remedied by digestive enzymes that break down the fructans in onions– like FODZYME or FODMATE.
If sulfur is the issue, you may find that supplemental molybdenum (a mineral involved in sulfur breakdown pathways in the body) can help to improve your oral tolerance to some higher-sulfur foods (like onions), at least to a certain extent. (Consult your treatment team for customized recommendations!)
Low FODMAP onion servings and swaps
Another option is low FODMAP variations of onions– like green onions, or scallions and chives. They taste very similar to onions, and can add a similar flavor without the gases and fermentation that follow regular onions or onion powder.
- For example, I incorporate green scallions and chives instead of regular onions for a burst of color and onion-like flavor in my low FODMAP chicken salad and low FODMAP egg salad recipes.
- If you cook with onion powder, one of my favorite low FODMAP onion powder products on the market is Gourmend green onion powder.
- See how your body reacts to a low FODMAP serving– two tablespoons or less of diced Vidalia onions– as part of a low FODMAP egg-veggie scramble or stir-fry.
- Make your own onion-infused olive oil, which adds onion flavor without the fermentable fructans found in onions.
Cooked (versus raw) onions
If you have trouble digesting the fibers and roughage of raw onions (this is common in cases of inflammatory bowel disease), you may find that eating soft-cooked onions in soups or stir fry dishes is better tolerated. (I love adding cooked onions to my eggs and pasta dishes!)
You may still want to start with low FODMAP servings of cooked onions, and titrate up the dose gradually based on your oral tolerance.
A root-cause approach
No matter what’s causing your onion intolerance, make sure to also address the underlying root cause of the fructan intolerance– which is usually, in my experience, a microbial overgrowth in the gut. Work with your treatment team to rule out underlying gut imbalances such as:
- Small intestinal bacterial overgrowth (SIBO)
- Dysbiosis
- Mold illness
- Intestinal methanogen overgrowth (IMO)
- Inflammatory bowel disease
You may also want to consider nutrigenetic testing for exceptionally customized food and supplement recommendations.
Recap and Final Thoughts
Even though onion intolerance is a common type of adverse food reaction among people with IBS and other types of digestive disorders, onions and IBS are not mutually exclusive. There are work-arounds and loop holes if you would like to keep onions in your diet.
Work with your treatment team of healthcare providers (such as a gut health dietitian and a gastroenterologist) to help you determine whether you’re reacting to the fructans, sulfur, and/or fiber in the onions– and take action accordingly.
Consider enzyme replacement and digestive support, low FODMAP variations and serving sizes of onions, and/or cooking onions to make them more compatible with your digestive system during this season of your healing journey.
Lastly, don’t forget that everything happens for a reason– including food intolerances. It’s not recommended to stay on a low FODMAP diet (even if it’s helpful) long-term. Your healthcare team should be guiding you to identify the underlying reason for your adverse food reactions so you can address and resolve this issue at the root-cause level.
Next Steps
For folks with onion intolerance
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