The health benefits of onions

Healing properties abound - nutritionist Jo Lewin divulges the nutritional benefits, medicinal properties and teary secrets of the humble onion.

An onion sliced in half and into rings on a chopping board

An introduction to onions...

The humble onion is found in every kitchen, but its curative powers make it an important medicinal plant too. Like garlic, it is a member of the lily family. There can be no doubting the power of the juices contained in onions; anyone who has ever sliced one and shed a tear is only too aware that they hold something special. Quite apart from its medicinal properties the onion is simply delicious. It forms the basis of so many dishes - whether raw, sautéed, baked, steamed or boiled, that it would be difficult to imagine the cuisine of any country without it.

Ancient healing...

Red onions
Onions were historically used as a preventative medicine during epidemics of cholera and the plague. They were apparently eaten by Roman emperor Nero as a cure for colds, and its reputation has made onions a popular component in the diets of many countries.

...The onion's revenge: The smell of onions can be a problem, both on the hands and on the breath. After chopping onions, try rinsing the hands with cold water, rubbing them with salt, rinsing again and then washing with soap and warm water. To remove the smell from breath, eat a few sprigs of parsley or an apple to help conceal the odour.

Nutritional highlights

More than just a tasty culinary plant, the onion contains natural sugar, vitamins A, B6, C and E, minerals such as sodium, potassium, iron and dietary fibre. In addition, onions are a good source of folic acid.

100g serving of onions contains:

  • 35 calories
  • 8g carbohydrate
  • 6.2g sugars
  • 2.2g fibre

The power of raw...

Onion being chopped
The reason that the onion is so much more active in its raw state than when cooked, is that it contains a variety of organic sulphur compounds, contained in a volatile oil, that provide the health benefits. These are partly destroyed by heat. When eaten raw, its juice can act as an irritant and some people find it difficult to digest. Those who are not tempted by the idea of eating raw onions can follow simple cooking methods that may make them more palatable. For people with sensitive stomachs, this is a far more suitable way to enjoy the health benefits of onions. Onions baked in their skins, in a similar way to baked potatoes, are also delicious. This method of cooking keeps all the goodness inside, but the resulting flavour is milder and more aromatic than that of raw onions.


Although not nearly as valued a medicinal agent as garlic, onion has been used almost as widely. Onions have been used in folk medicine for the relief of coughs, colds and catarrh, especially asthma, but more recently some of their curative properties have been attributed to a compound called allyl propyl disulphide, which is thought to have a similar effect to insulin in balancing blood sugar levels. This does not mean that the onion can be used as a substitute for insulin therapy; but it may be of help to those who suffer from hypoglycaemia. If you suffer from hypoglycaemia consult your doctor if you have any nutritional queries.

Types of onions

Leeks cooked in pan
Onions differ in the size, colour and taste. Spring onions are grown in warmer climates and have a milder, sweeter taste. Storage onions are grown in colder weather climates and generally have a more pungent flavour and are usually named by their colour: white, yellow or red. Smaller onions come in many types, such as chives, leeks and shallots.

How to select and store

Globe onions should be clean and hard and have dry, smooth skins. Avoid onions in which the seen stem has developed. Also avoid those that show signs of decay. Onions should be stored at room temperature, away from bright light and in a well ventilated area. Those that are more pungent in flavour such as yellow onions, will keep longer than those with a sweeter tastes such as white onions, since the compounds that produce the sharp taste are natural preservatives as well. All onions should be stored away from potatoes, as they will absorb their moisture and ethylene gas, causing potatoes to spoil more easily. Do not store cooked onions in a metal bowl or storage container as this will cause them to discolour. Freezing chopped onions will cause them to lose much of their flavour.

Cry me a river...
...the compound allyl sulphate which is produced when an onion's ruptured cells are exposed to air is responsible for producing tears. To reduce the production of this compound, chill the onions for half an hour or so before cutting to reduce the activity of the enzyme.

Recipe suggestions

Onions feature as the basis of many classic recipes worldwide. Here are just a few ideas:

Cheese & onion is a partnership not just for crisps:
Easy cheese & onion slice
Cheese & onion pork chops
Caramelised onion & feta pizzas
Cheese & onion soufflé tart

Onion transforms gravy:
Sausages with sticky onion gravy
Sausages with quick onion gravy

Raw onions for the brave and the bold:
Tuna & red onion salad
Tomato & onion salad

Onion soups:
Pea, mint & spring onion soup with Parmesan biscuits
Caramelised onion & barley soup with cheese croutons
Onion soup with herby garlic cheese bread

And let's not forget the classic onion ring!
Crispy Cajun onion rings

This page was last reviewed on 24th September 2018 by Kerry Torrens.

Kerry Torrens is a qualified Nutritionist (MBANT) with a post graduate diploma in Personalised Nutrition & Nutritional Therapy. She is a member of the British Association for Nutrition and Lifestyle Medicine (BANT) and a member of the Guild of Food Writers. Over the last 15 years she has been a contributing author to a number of nutritional and cookery publications including BBC Good Food.

Jo Lewin is a registered nutritionist (RNutr) with the Association for Nutrition with a specialism in public health. Follow her on Twitter @nutri_jo.

All health content on is provided for general information only, and should not be treated as a substitute for the medical advice of your own doctor or any other health care professional. If you have any concerns about your general health, you should contact  your local health care provider. See our website terms and conditions for more information.

Comments, questions and tips

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Robert Windermere's picture
Robert Windermere
14th Jan, 2019
I must say, whenever I cook with red onions, I always find myself snacking on a few bits when I'm chopping them! Can't get enough of them, although my wife is never happy should she try and kiss me afterwards! XD Really interesting information about their health properties though, and some interesting storage information. Had been using this guide (, but had no idea about not putting them near potatoes!
4th May, 2017
Onions are the best, they are so tasty and they blast your mouth when eaten raw, with their hot spicy and feiry juice. Onions go so well with food, fried with mushrooms, delicious and roasted, so tasty.
Robert Newton
9th May, 2016
In Jamaica we use onions and red peppers in most of our dishes. Fried escovitch fish with lots of onion slices, and our favorite sunday morning dish calaloo. We also like to use onions to make pickle.
Robert Newton
9th May, 2016
In Jamaica we use onions and red peppers in most of our dishes. Fried escovitch fish with lots of onion slices, and our favorite sunday morning dish calaloo. We also like to use onions to make pickle.
17th Apr, 2015
In India we use onions in almost every spice rich recipe. Onion salad with tomato and cucumber tastes very good. Apart from its added taste to food items I understand from this article that it offers nutritious contents along with medicated values. True onion is a good food supplement.
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