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Onions contain a range of vitamins, minerals, prebiotics and potent plant compounds shown to promote health in many ways. Dietitian Dr. Linia Patel summarises the health benefits of onions and why they may trigger IBS in some people.


Onions are an ingredient in all our non low FODMAP meals but is not used the creation of any of our low FODMAP meals.

Interesting facts


Onions are members of the Allium genus of flowering plants alongside garlic, shallots, leeks and chives. Domesticated alliums first emerged in Asia but then spread across the continents as they propogate easily, grow reliably and can be stored for months. Onions were staple foods of the ancient Egyptian labourers responsible for the pyramids of Giza and onions are even portrayed in some of the tomb decorations. Aliums were brought Britain by the Romans where they became a staple for both kings and ploughmen.
Turns out there is nothing to cry over, the medicinal properties of onions have been recognised since ancient times when they were used to treat ailments like headaches, mouth sores and even heart diseases.

Rich in


  • Vitamin C
  • Vitamin B6
  • Potassium
  • Quercetin
  • Fibre
  • Prebiotics - inulin, fructooligosaccharides

Key health benefits



  • Antioxidant powerhouses. Quercetin the phytochemical that’s highly concentrated in onions has potent antioxidant properties. In addition, other abundant sulphur compounds (sulfides and polysulfides) and vitamin C in onions also act as antioxidants. Antioxidants protect cells against aging and disease (1).
  • Support healthy digestion & your immunity. Onions are a rich source of prebiotics called inulin and fructooligosaccharides which contribute to improved digestive health and better immune function (2,3). These prebiotics that may however cause digestive problems in some people who suffer with IBS (4).
  • May reduce inflammation. Low grade inflammation raises the risk of many chronic disease like type 2 diabetes, heart disease and cancer. Onions are a rich source of fibre which is broken down by beneficial gut bacteria to produce beneficial by-products. These by-products not only strengthen your digestive system but reduce inflammation too (5).
  • Lowers risk of heart disease. Plant compounds found in onions have been found to decrease levels of “bad” cholesterol. Their anti-inflammatory properties may also help reduce high blood pressure and protect against blood clots – all of which may lower your risk of heart disease (6).
  • Contains cancer fighting properties. Eating vegetables of the Allium genus like onions has been linked to a lower risk of certain cancers, including stomach and colorectal (7).
  • Blood sugar regulation. Specific plant compounds found in onions like quercetin and sulphur compounds may possess effects that help control blood sugar levels (8).

If you are on the low FODMAP diet



Onions may aggravate bloating if you have a Irritable Bowel Syndrome (or a sensitive tummy) as onions are rich in fermentable carbohydrates called fructans. They are not advised, for this reason, when you are following the elimination stage of the low FODMAP diet. This is often quite tricky as onion is used in many recipes and a key ingredient in most sauces, soups and Italian meals.

  • Suitable alternatives. It is possible to cook flavoursome meals without onion. Try adding chives or the green leaves on your leek or spring onion instead. Hing or asafoetida may also help you capture that onion flavour without any of the fructans.
  • Please reintroduce onion. Fructans are a good prebiotic for your gut bacteria so it is advised that you do reintroduce onion after you have completed the elimination of 6 weeks. Under the guidance of a dietitian you will be do some onion challenges to see if onion is a trigger and how much you can tolerate in one meal.

Chef's tips



  • Colourful varieties such a red or yellow onions are packed with more antioxidants than white ones.
  • Put an onion in the freezer for some time (without freezing it) before you chop it to reduce the 'cry-factor'.
  • Use onion as a base for stocks and soups.
  • Add thinly sliced red onions to our favourite salad.

Dr. Linia Patel

Registered dietitian

IG: @liniapatelnutrition

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