Onion & Garlic - Intolerance or Allergy?

Onion & Garlic - Intolerance or Allergy?

Written by Shaynie Ashkenazi ANutr. BSc. MHumNutr. Registered Associate Nutritionist (ANutr.), Founding Director, FodShop.


Onions & garlic are delicious, popular additions to many meals we know and love in many cuisines across the world.

If you know you can't tolerate them and you're making a conscious effort to avoid them, you may quickly find, however, that they’re extremely difficult to avoid in most prepared and packaged foods. They're found in virtually all ready-to-eat meals, snacks, seasonings, bottled sauces, condiments and more!

Onions are part of the genus allium plant, along with garlic, chives, and shallots. It's therefore not surprising that those sensitive to onions also react to other allium vegetables as well.

Allergy or Sensitivity: What's the Difference?

Having a true onion or garlic 'allergy' is rare.

Upon consumption of the vegetable's flesh, an allergic reaction is triggered by the immune system with the release of histamines, causing a range of systemic reactions in the body, some of which can be fatal, such as anaphylaxis. 

Having an onion or garlic intolerance means that the digestive system reacts to the maldigestion of the 'fructans' i.e. FODMAPs found within onion and garlic. No immune response follows.

All humans naturally lack the enzymes - 'fructanases' - necessary to digest fructans, therefore those who experience the familiar symptoms of bloating, diarrhoea, constipation etc.. are considered 'hypersensitive' to fructans i.e. they are experiencing a phenomenon called 'visceral hypersensitivity'.

Food intolerances usually cause less severe reactions than food allergies. If you have a fructan intolerance, your immune system will not be triggered, however many of the same symptoms of allergy which present in the gut i.e. bloating, abdominal pain, alternating bowel habits etc.. will be triggered as a result of the bacterial fermentation of fructans in the large intestine.

So Am I Reacting to Alliums or FODMAPs?

If you’re experiencing digestive symptoms in response to consuming onion, garlic, and/or any other vegetables in the genus allium family, it may be difficult to identify if you are experiencing a sensitivity to allium compounds (a type of food chemical) or an intolerance to fructans, as both molecules are found in this family of vegetables.
You may experience internal or external symptoms, which can range from mild to severe, and can vary in terms of onset.

Anecdotally, symptoms of allium intolerance may include the gut, and can involve:

  • Difficulty breathing
  • Nausea and vomiting
  • Diarrhoea
  • Increased heart rate
  • Stomach pain
  • Cramping
  • Gas
  • Dizziness or light-headedness

Symptoms of fructan intolerance always occur in the gut, and can involve:

  • Gas
  • Bloating
  • Cramping & abdominal pain
  • Belching
  • Constipation
  • Diarrhoea

Symptoms resolve once the onion/garlic is no longer in the system.

If you have severe reactions such as vomiting or gastric distress that doesn’t stop, dizziness, or trouble breathing, seek immediate medical attention by calling 000.

So Can I eat Onion & Garlic After All?

In food intolerance, the quantity of the food poorly tolerated is able to be modified to achieve gut symptom control.

You should make a visit to your FODMAP trained Accredited Practising Dietitian to ascertain how much, if any, onion and/or garlic you can tolerate in relation to your own personal tolerance threshold.

If you find you cannot tolerate any onion or garlic at all, you can achieve the same depth of flavour offered by onion & garlic, in various ways.

For the sweetness of softened garlic and caramelised onion, experiment with paprika, cumin or sugar. Some of the umami that comes with the addition of alliums can also be achieved by adding fish sauce, soy sauce, or grated ginger and chilli.

Some ingredients to experiment with if you’re intolerant to allium and/or fructan:

  • Lemon zest
  • Asafoetida
  • Coriander
  • Chilli
  • Ginger
  • Soy sauce
  • Fennel
  • Celeriac
  • Cumin
  • Miso
  • Fish sauce

Onion & Garlic Replacers Available at FodShop

FodShop stocks a range of onion & garlic replacer products, including:

Please note that these products contain allium compounds. If you have a known allium hypersensitivity or you are allergic to onion or garlic, please do not consume these products.

These products are free from, or extremely low in fructans i.e. they are low in FODMAPs. They have been laboratory tested and proven to be low in FODMAPs per serving of each product, therefore they have successfully earned the Monash University Low FODMAP Certification or the FODMAP Friendly Food Program Low FODMAP certification.

If you have a known intolerance to fructans, these products are all suitable to consume while following a low FODMAP diet.

Where To From Here?

In order to ascertain whether or not you are intolerant to fructans and/or allium compounds and/or allergic to onion or garlic, it is important you undertake the necessary diagnostic testing via referral to an Allergist or other specialist practitioner.

If you suspect you have an intolerance to onion and/or garlic, visit your FODMAP trained Accredited Practising Dietitian to discuss the appropriateness of undertaking a FODMAP elimination diet.

If you have not had the chance to visit a dietitian as yes, please view our global online directory to get started for success.


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