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Onions are something everyone should have some knowledge of. They’re an incredible plant, a real taste bomb, and sure to benefit your health in some way. The health benefits of onion have been known about and utilized for centuries. Valuable knowledge that has sadly become less and less known about. So read on and enlighten yourself, your overall health and tastebuds will definitely thank you for it.various onions in basket on table

A little bit about onions

The onion is a species of vegetable of the Allium genus. Due to its incredible flavor, it’s widely cultivated for culinary purposes throughout the world.

The plant itself consists of long, hollow green leaves above, and a short fat roundish bulb below with roots growing beneath it. Both parts of the plant can be eaten. The big round bulb part is what we know as the onion. 

There are different varieties of onion such as white, red, and yellow. The yellow variety is what most of us know as the common onion.

Close relatives of the onion include garlic, leek, shallot, and chive.


Is onion good for you?

Without a doubt, onion is definitely good for you and will benefit you in many ways. It’s just jam-packed with health benefits deriving from all the vitamins, minerals, and antioxidants they contain. Some of these health benefits you may be familiar with, others you probably won’t be. 

Different onion types and antioxidant content

The health benefits of onion, nutritional content, and appearance differ slightly for the three most commonly used varieties. Interestingly, a 2019 study discovered a notable difference in the antioxidant content between the different varieties of onion. As antioxidants are very beneficial for our health it’s worth knowing which onion type typically contains the most.

Another very noteworthy discovery from the 2019 study was how the antioxidants themselves are physically distributed throughout the onion. The antioxidants in any onion are most concentrated in the outer layers, decreasing gradually toward the center of the bulb. Interestingly most of us will discard the outer layers of an onion when preparing them, potentially throwing away the best part in terms of health benefits.

  • Red Onion

Easily distinguishable from white and yellow onion by their dark red/purple color. Their color actually comes from the antioxidant anthocyanins. Some red onion varieties contain up to twice as many antioxidants as some white or yellow onions. For general health antioxidants are very beneficial, so a double dose of these is going to do you no harm at all.

  • White Onion

These are sweeter and milder than your more standard yellow onion. Identifiable from yellow onions by their flakey, papery, white skin. Generally speaking, a white onion will have a lower antioxidant content than most red or yellow varieties.

  • Yellow Onion

Our most common variety of onions. Identifiable by its thick yellow and almost brown-looking skin. The overall antioxidant content of yellow onion somewhere between red and white onion.

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The difference between Scallion, Spring Onion, and Green Onion?

When the onion plant is young, before the bulb begins to develop in size, the green leaves along with the little bulb can be harvested and eaten as scallion, green onion, or spring onion. The only difference between these is the maturity stage, going from youngest to oldest respectively. Although the taste of these is generally milder, the nutritional content and health benefits are pretty much similar to normal onions.

There is a particular species called Allium fistulosum that is used only for scallions etc. In this species, the bulb never develops much past the width of the green leaves. Generally speaking though scallions, green, and spring onion can be derived from any species of young onion.

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List of health benefits of onion

There are many great health benefits of onion. Below are just some of the real-world health benefits you can start enjoying immediately by consuming onion regularly.

Benefit #1 – Regulates blood sugar

Onion has an amazing health benefit in the form of helping to regulate blood sugar. That is particularly of interest to those with diabetes or prediabetes. Diabetes is a condition that causes sugar to build up in the blood to the point that it becomes a problem.

A 2010 study on the use of red onion on type 1 and type 2 diabetic patients revealed some very interesting results. Two points of reference were used –

  1. Fasting blood glucose level
  2. Hyperglycemia level 
Reductions in Type 1 Patients
TreatmentFasting Blood GlucoseHyperglycemia
Insulin145 mg/dl153 mg/dl
100g Red Onion89 mg/dl120 mg/dl
Watern/a77 mg/dl
Reductions in Type 2 Patients
TreatmentFasting Blood GlucoseHyperglycemia
Glibenclamide81 mg/dl114 mg/dl
100g Red Onion40 mg/dl159mg/dl
Watern/a55 mg/dl

In its conclusion, it stated as evident that crude red onion produced hypoglycemic effects, and so could be used as a dietary supplement for the management of type 1 and 2 diabetes.

Benefit #2 – Increases bone density

Regular consumption of onion may help to increase your bone density. A particularly important health benefit, especially as we get older. As we go past 50 bone density tends to decrease, and the risk of osteoporosis increases.

A 2009 study of over 500 postmenopausal and perimenopausal women backed up the claims of onion’s ability to improve bone density. It found that bone density increased in relation to how often the subjects consumed onion. It was discovered that the bone density of those who consumed onion once a day was 5% greater than those who consumed it once a month or less. The study also revealed that the most frequent consumers of onion had a 20% reduced chance of hip fracture compared to those who consumed no onion at all.

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Benefit #3 – Helps with heart health

One of the great health benefits of onion is that it may help with heart health. As we now know onion is full of antioxidants.

A strong anti-inflammatory flavonoid antioxidant called quercetin is particularly concentrated in onions. Quercetin has been shown to lower blood pressure in overweight people in a 2015 study. In the double-blinded placebo-controlled study 70 overweight test subjects were randomly given either a placebo or 162 mg/d of quercetin from onion skin extract powder. The study concluded that the quercetin treatment lowered blood pressure in patients with hypertension, and suggested a cardioprotective effect of quercetin.

Most of the quercetin content in the onion is found in its outermost layers. Quercetin is also much higher in red and yellow onion than white onion. Worth keeping in mind if trying to reap the benefit of quercetin from an onion.

Another antioxidant found in onions that may benefit heart health is anthocyanins. Particularly high in red onions as it contributes to their coloring. Several studies have suggested a link between high anthocyanins intake and reduced risk of fatal heart attacks.

A 2013 study was conducted on 93600 women between the ages of 25 and 42. The study concluded that a high intake of anthocyanins may reduce the risk of a heart attack by as much as 30%.

A 2016 study was conducted on 43000 healthy men with no prior cardiovascular disease (CVD) or cancer. The results of the study concluded a high intake of anthocyanins may reduce fatal heart attack risk by around 14%.

Benefit #4 – Improves immune system

Onions are very high in vitamin C with 100g giving you 7.4 mg, or 8% of your RDA. Vitamin C is a critical fuel for your immune system. This in addition to all the other vitamins, minerals, and antioxidants keeps your immune system in peak condition. This will ensure you keep those colds and flues at bay.

Benefit #5 – Helps with vision

Onions contain a protein that’s high in sulfur called glutathione and the antioxidant quercetin.

Glutathione is known as a fantastic antioxidant for the lenses of your eyes. It helps with protecting your eyes from disease and keep them healthy. This protein helps with keeping things such as cataracts, macular degeneration, and glaucoma at bay.

The antioxidant quercetin is a natural remedy for both eye inflammation, and eye irritation.

If you suffer from dry eyes you can use onions ability to make you cry to gently stimulate your tear ducts. This will provide much-needed moisture to your eyeballs. Obviously, you’ll want to proceed gently with this method. Don’t just put a sliced onion to your eye until you can no longer bear it. That would be more of a torture than a treatment! Pull back when you feel the tears coming and repeat as needed.

Overall onions have many benefits for your eye health.

health benefits of onion - helping vision image

Raw onion vs onion powder

As we know there are many health benefits of onion. We also know they can be a bit of a pain to prepare, especially if you’re tight on time. Wouldn’t it be great to have all the goodness of onion in a pre-prepared powder format? Welcome to onion powder. The question though – is it as good as using real onion?

Onion powder is way more concentrated than raw onion. So, how much onion powder equals one onion? Answer – 1 tablespoon of onion powder is equal to 1 cup of raw onion. Onion powder is dried onion ground down to a powder. This can be every part of the onion including skin and roots, and here lies something interesting to consider.

As we know by now the antioxidants found in onions are more concentrated in, and toward the outer parts of an onion. Most people when using fresh onion will discard these outermost layers. Throwing away a lot of the good health benefits in the process. So, depending on how the drying process affects those antioxidants, onion powder may have an edge over using raw onion in this regard.

Overall I would say that onion powder will be better than using no onion at all if time isn’t on your side. It’ll also be a good option for installing a flavor kick to your meals. All that being said though I would always recommend using the raw version instead of powder as much as possible, and as close to the skin as you can realistically manage.

FAQ about Onion

Find a quick answer below to some frequently asked questions about onions.


FAQ #1 – Is onion a vegetable or fruit?

For those of you wondering – yes onion is a vegetable and not a fruit.

FAQ #2 – How to cut an onion without crying?

There are many different opinions on how to achieve this. Some of which work and some that don’t. However, there seems to be a common consensus on the following methods – 

  • Using a very sharp knife to cut with.
  • Chilling the onion before cutting.
  • Use a fan or cooker extractor hood to blow or suck fumes away from you.

FAQ #3 – How long do onions last and how should you store them?

The ideal condition for onion storage is a cool and dry place. The table below will give an idea of how long you can expect onion to last under different storage conditions.

How long onions can last in different storage conditions
Onion preparation stateStorage conditionLength of time
Raw (whole)45 – 55 degrees F (7 – 12 degrees C )Up to 3 months
Raw (whole)Room temperatureUp to 1 week
Raw (whole)FridgeUp to 2 weeks
Raw (Chopped, or Sliced)A sealed airtight container in the fridgeUp to 2 weeks
Cooked (Chopped, or Sliced)A sealed airtight container in the fridgeUp to 4 days
Raw (Chopped, or Sliced)FrozenUp to 8 months
Cooked, (Chopped or Sliced)FrozenUp to 12 months

FAQ # 4Is onion bad for dogs?

This question is slightly off-topic in terms of the health benefits of onion. However, it’s certainly worth mentioning as many of us have dogs, and might be unaware that onion poses any risk to them.

There’s a compound in onion known as N-propyl disulfide. It causes your dog’s red blood cells to break down, and your dog will begin to suffer anemia as a result. So, keep this in mind when feeding your dog any leftovers, and keep them away from onion as much as possible.


So, without a doubt consuming onion will benefit your health. They can be a bit of a pain to prepare but like they say – no pain no gain! In this instance, the gain from health benefits will definitely outweigh the pain of chopping, slicing, crying, etc.

Onion is such a versatile and flavorsome food that there really is no excuse to not add it to your diet a few times a week. People often worry about having to make a massive change to their diet to get started. Something as simple as popping some raw (or cooked) onion on top of your burger, or into your pasta is a great place to start. Small things like this don’t require huge changes at all and get you started on a much healthier lifestyle.

If you’re interested in other natural foods packed with numerous health benefits then check our other articles about mint, honey and lemon water, and green coffee.

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Always consult your GP before undertaking any form of weight loss, fitness, or exercise.

Michael Duffy
Michael Duffy

Fitness, health, and outdoor enthusiast! 2 decade of experience training for, and competing in different sports. Boxer, runner, road cyclist, triathlete, and XC mountain biker. More about me here.

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