Onion is the most widely cultivated species of Allium. Garlic, Chinese onions, leeks, and chives are its close relatives.

They are also known as Pyaz in Hindi, Vaengayam in Tamil, Pyajj/Piyaz in Bengali, Savala (Malayalam), and Kandaa (Marathi).

Evidence suggests that onions were used as far back as 5000 BCE in China. 

Onion has bluish-green leaves and bulb at the base, bulb start to grow underground when the certain day is completed. The bulb is made of small and compresses underground stem surrounded by leaves.

Onion is cultivated around the world and used as the main food ingredient in many countries. They can be used as a cooked vegetable, can be eaten raw in a salad or can be used to make pickles.

Now let’s talk about onion on a ketogenic diet.

Nutrition facts of onion

nutrtion in onion, carbs in onion

Raw onion’s most weight is due to its water weight. Onion weight 89% water and  9% carbs, 1.7% fiber and the rest are due to protein and fat.

All the nutrition facts are taken from the USDA Food Composition Databases. Nutrients in 100g raw onion are. 

  • Calories  40
  • Carbohydrates 9.3g
  • Fiber  1.7g
  • Water 89g
  • Sugars  4.2g
  • Protein  1.1g

Vitamin and minerals 

  • Vitamin C – it contains 7.4 mg or 12% of the RDI value for vitamin C. This vitamin is needed for the maintenance of skin and hair, and essential for immune functions.
  • Vitamins B6 – it contains 0.1 mg or 6% of the RDI value for vitamin B6. this vitamin is needed for the formation of red blood cells.
  • Folate – it contains 19 mcg or 5% of the RDI value for folate. It is a water-soluble B vitamin and it is essential for metabolism and cell growth.
  • Potassium – it contains 146mg or 4% of the RDI value for potassium. It is helpful with heart health.
  • Manganese – it contains 0.1mg or 6% of the RDI value for manganese. 

Other compounds 

  • Quercetin – improve blood pressure and heart health.
  • Sulfur compound – may protect against cancer. [1] [2]
  • Thiosulfinates – inhibit harmful microorganisms and prevent the formation of blood clots. [3]

All these nutrients make onion one of the best foods on a keto diet

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Onions and a Keto Diet –  can you eat onion on a keto diet?

Not all vegetables are allowed on a keto diet. Keto diet is a low carb diet that helps you to stay in ketosis. As we selecting vegetable for a keto diet, we also put one eye on net carbs.

Onions are also contained a low, moderate amount of carbs as we have discussed above. The answer is not that simple. 

Uses of onion on a keto diet depends on some other factors.

Those who have just started a keto diet and haven’t yet fully adapted ketosis state, they should stick to the basic ketosis diet and should not try new experiments. Onions do not contain fat, so they cannot be good for your ketosis. Because other foods that are high in fat also contain a few carbs. And adding onion can cross the 20g carbs limit.

But once you are in ketosis and you have adapted ketosis fully.

Now, you can check your carbs tolerance limit by adding a little bit onion to your keto diet. It also depends upon your lifestyle and how much calories you burn. If you are an athlete you can eat up to 50g carbs without getting out ketosis. 

But remember, before adding any carbs to your diet, make sure that you are in ketosis. You can check the blood ketone level.

  • Partial ketosis – 0.5 mmo/L. This means you are not in full ketosis yet. It is not the right time to add carbs to your diet.
  • Optimal ketosis – 1.5 – 3.0 mmo/l. This means you are in ketosis. You can test your carbs’ tolerance limit and try to add some carbs to your diet. This ketone zone is optimal for weight loss.
  • High ketosis – greater than 3.0 mmo/l is best for therapeutic. You should try it under supervision.

You can check the blood ketone level with a blood ketone meter.

If you are in ketosis and want to add onion to your diet. The best onions for ketosis are:-

  • Green onions 3.9g net carbs
  • Scallions (spring) onion 3.7g net carbs
  • Yellow Onions 6.1g net carbs
  • Sweet onions  6.6g net carbs

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Fast facts of onion

  • Onion cultivation started 5500 years ago in some parts of Asia.
  • It’s some of the oldest vegetables that were used by modern civilization
  • Largest anyone ever founded weight around 5kg.
  • Onion is 6th most popular vegetables in the world with its production
  • Yellow onion is the most popular type of onion. About 75% of total world onion production

How many onions can eat on a keto diet?

The main reason you are trying a keto diet to stay into ketosis. Once you have adapted ketosis fully, It doesn’t mean you go crazy on carbs.

Carb limit on ketosis varies from person to person, on their activity level, lifestyle, energy need. But carbs limit below 20g is safe for everyone.

If you are lifestyle is sedentary, it is better for you to eat less than 20g a day and you should try to increase the carbs limit.

  • A small onion can weigh around 4 ounces or around 125g.
  • A medium onion can weigh around 6 ounces or 150g to 170g around. 
  • A large onion can weigh around 8 ounces or 225 to 250g.

So, you should eat a maximum of half medium onion on a standard keto diet (carbs<20g). But if your activity level is high so you can eat up to one medium onion. 

It will be better if you eat scallion or yellow onion on your keto diet.

The bottom line is you eat more tasty vegetables as you increase your activity level. If you are a general person with moderate activity, you should no more than half an onion. Because in your keto diet other foods will also contain few carbs.

Which type of onion is best for a keto diet?

best onion on keto diet, net carbs in onions,

There are different types of onion. We can find onion in different sizes, tastes, and odors. Different types of onions grow in different countries. But we are here to find the answer to the question of which type of onion is best for the keto diet? So, our main focus will be on net carbs.

1. Yellow Onions

It is the most popular type of onion by production. About 75%of total world onion production.

It has ivory white flesh which is surrounded by heavy brown skin, with strong sulfur pungent flavor and aroma. In many countries, it is a common and necessary ingredient of cooking recipes.

It is also very rich in vitamins K and C.

Total carbs – 7.8gFiber – 1.7g    Net carbs  – 6.1gServings – per 100g

Source – USDA Food Composition Databases.

Amount on a keto diet – in moderation, as long as you can keep under the carb limit 

Best to eat on keto – best after keto-adaptation stage

2. Sweet onions

They have lighter and less-opaque skin. They are larger and flatter than a yellow onion. It does not contain a punch of sulfur compounds. It tastes sweet due to the absence of sulfur. They contain a little bit of extra sugar. It contains 5g of sugar per 100g. But it’s fine. You can use them on keto.

Total carbs – 7.5gFiber – 0.9g    Net carbs  – 6.6gServings – per 100g

Source – USDA Food Composition Databases 

Amount on a keto diet – in moderate amount, as long as you can keep under the carb limit.

Best to eat on keto – best after keto-adaptation stage

3. White onions 

They have white skin. They are milder and sweeter than yellow onions. If you like raw onion, then it can be best for you. They are difficult to store. In some countries, white onions are used in every dish.

Total carbs – 10gFiber – 1g    Net carbs  – 9gServings – per 100g

 Source – myfitnesspal

Amount on a keto diet – low amount

Best to eat on keto – After keto-adaptation stage

4. Red onions

These are purplish skin-red skin and white flesh tingles with red. These onions are medium to large size and sweet enough to eat raw. They often consumed raw, cooked with other food or decorated in a salad. They are high in fiber and flavonoids. Easier to store and can be easily stored for 2-3 months at room temperature. 

Total carbs – 9gFiber – 2g    Net carbs  – 7gServings – per 100g

Source – myfitnesspal

Amount on a keto diet – low amount

Best to eat on keto – After keto-adaptation stage

5.  Scallions (spring) onion

Mostly used in Asian and European countries. You can use the leaves and bulbs both on a keto. It has a tender aroma than other onions. It contains lots of vitamin K. it contains 259% of RDI values for vitamin K. other than that it is also rich in vitamin A, C, folate, and riboflavin. [4]

Totals carbs – 7.3gFiber – 2.6g    Net carbs  – 3.7gServings – per 100g

Source – USDA Food Composition Databases

Amount on a keto diet – As much you want (keeping limit under 20g carbs limit)

Best to eat on keto – at any stage

6.  Green onions

These are immature onions. In these, bulbs haven’t formed yet. The entire plant can be used including green shoots. They usually make wonderful soups, tocos, and soups.

Total carbs – 5.7gFiber – 1.8g    Net carbs  – 3.9gServings – per 100g

SourceUSDA Food Composition Databases

Amount on a keto diet – As much you want (keeping limit under 20g carbs limit)

Best to eat on keto – at any stage

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How to use onion on a keto diet?

1. Shredding 

You should shred the onion rather than cutting in a circle. Using shredding can easily stay below-allowed limit. Using this way its flavor will be unchanged.

2. Cooking at low temperature rather than high temperature

Cooking at a high temperature can cause loss of ingredients. Try to cook onions at a low temperature and it will be beneficial for your health on a keto diet.

3. Try to avoid onion circle

Using an onions circle can easily cross the 20g limit.

4. Avoid caramelizing

Caramelizing should be avoided completely because it is being noticed that caramelized onion can increase blood sugar levels. So always use raw or lightly cooked onion on a keto diet.

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Benefits of onion

You should know how much benefit of onion and why you should consider adding onion to a keto diet.  You know how many minerals and vitamins it contains. Now it’s time to know a little bit about the health benefits of onions.

  • Onions contain antioxidants that can help to decrease blood pressure and cholesterol and ultimately decrease heart disease risk. [5, 6, 7]
  • In several studies, it was found that onions contain a compound that can help to fight with cancer.
  • Evidence suggests that onion can help with lower blood sugar levels. [8] [9]
  • Onions can inhibit the growth of dangerous bacteria such as Escherichia coli, Pseudomonas aeruginosa, and S. aureus.
  • Onions are high in vitamin C that can be good for your skin and hair health.
  • They also help in folate that can help with depression.
  • Chewing raw onion can help with oral health.
  • Onion is a great source of antioxidants. It contains more than 25 different antioxidants. They can help to reduce heart attack risk. [9] [10]


Onions are loaded with vitamins, minerals, and antioxidants that can be very beneficial for your health, especially on a keto diet which is very restrictive.

But if you are just getting into ketosis or on ketosis adapting stage, you should avoid any extra carbs included onions.

If you are in optimum ketosis (confirm with a blood ketone test) then you can consider adding carbs. 

First, add just half of the medium size onion or less to your diet After testing again blood ketone level and increasing your activity level you can add more onions to your diet.

Onion is a very delicious and nutrients dense veggie. You would love a keto diet after adding a small amount of onion.


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