Onion & garlic: friend or foe?

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By The Gut Health Doctor Team

Dr Megan Rossi in a lab looking through a microscope

It‘s becoming more and more common for us to see clients who have already excluded or trialled a removal of garlic and onion to aid their gastrointestinal (GI) symptoms.

So what’s the science and should we be avoiding them?

Garlic and onion both contain Fructans, a type of fermentable carbohydrate which is also a prebiotic (the food which feeds your good gut bacteria). This is a type of fibre that isn’t broken down in your GI tract and so moves from your mouth, past your stomach and small intestine and into your large intestine. It’s here in the large intestine that it’s fermented (broken down) by bacteria to produce beneficial byproducts which improve our immune health, mental health and metabolic health, to name a few.

For the majority of us, garlic and onion are beneficial, however, some people who have a sensitive gut or IBS may find that they can only tolerate a certain level of these products. In IBS, a hypersensitive gut may mean that when bacteria break down certain products in the large intestine, they trigger symptoms such as abdominal pain, bloating, flatulence or changes in bowel habits. Note that if you experience GI symptoms like these, you should have other conditions ruled out by your GP or gastroenterologist before making dietary changes. Ideally, you would then see a dietitian to help you, however, we know this is not feasible for everyone.

To test if you’re sensitive to garlic and onion, try the 3R method

R-emoving them for 4 weeks
R-ecord your symptoms
R-eintroduce them regardless of the result to assess your tolerance. Start with small amounts, slowly increasing and monitoring your symptoms.


  • Stock cubes, sauces, mixed herbs and savoury items often have small levels of garlic or onion added – check the ingredients list!
  • Use alternative herbs/spices to flavour your meals or garlic infused oil
  • If you’re sensitive, aim to include small amounts still to build up your tolerance: complete exclusion can increase your sensitivity

Take home

Garlic and onion have prebiotic benefits in your diet, and should be included to your own personal tolerance level, so friend or foe?! We say friend!


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