Used for:Stabilise blood glucose level, Treatment of colorectal cancer, Other bacterial infections, Prevention of osteoporosis in postmenopause
Chinese name:

What’s an Onion?

Onions are usually harvested in spring at central latitudes, and they belong to the Allium genus of flowering plants. Onions come in three types, yellow, purple, and white onions. Different types of onions have varied nutrients and tastes and are suitable for different cooking methods. Furthermore, the nutritional value and taste of raw and cooked onions are not the same. Raw onions taste spicy and contain a lot of selenium, which exhibits anti-cancer and antioxidant properties; whilst cooked onions taste fresh and sweet, and are rich in Scutellaria, which exhibits anti-inflammatory effects.


White onion
With white skin and white flesh.

Yellow/brown onion
With yellowish-brown skin and yellow flesh, larger in size.

Purple onion
With purplish-red skin and purplish-white flesh.


At central latitudes.



Nutrition facts

According to the Centre for Food Safety and Food and Health Bureau, the nutrition facts per 100 g of edible portion of raw onion, which is equivalent to ⅔ of an onion are:


40 kcal





Carbohydrates: 9.34 g

Sugars: 4.24 g

Dietary Fibre: 1.7 g (6.8% of DV)

1.10 g

Total fat: 0.10 g
Saturated fat: 0.042 g

Trans fat: NA

Cholesterol: 0 mg



Vitamin C: 7.4 mg (7.4% DV)

Calcium: 23 mg (2.9% DV)

Copper: 0.039 mg (2.6% DV)

Iron: 0.21 mg (1.4% DV)

Magnesium: 10 mg (3.3% DV)

Manganese: 0.129 mg (4.3% DV)

Phosphorus: 29 mg (4.1% DV)

Potassium: 146 mg (7.3% DV)

Sodium: 4 mg (0.2% DV)

Zinc: 0.17 mg (1.1% DV)

Recommended daily intake
Half an onion.

Health benefits of onions

Rich in antioxidant
According to the Journal of Agricultural and Food Chemistry, onions are one of the most abundant sources of flavonoids in the human diet. Quercetin is a type of flavonoid in onions that exhibits strong antioxidative power, it protects body cells from oxidative damage by free radicals and reduces inflammation.


Exhibit antibacterial properties
Quercetin in onions also helps inhibit the growth of harmful bacteria such as E. coli and S. aureus. In a test-tube study, quercetin extracted from yellow onion skin successfully inhibited the growth of bacteria by destroying the cell wall and cell membrane.


Promote bone health
Onions also help prevent osteoporosis by maintaining bone density. Studies have found that menopausal women who were accustomed to eating onions were about 20% less likely to experience hip fracture.


Control blood sugar
Onions are excellent sources of allicin, which regulates the secretion of insulin in the body to control blood sugar level. According to the National Institutes of Health, type 2 diabetes patients experienced a considerable reduction in fasting blood glucose levels after the consumption of red onion.


Allium vegetables such as garlic and onions are proposed to have an anti-cancer effect. A 2015 study published by Cancer Prevention Research revealed that allicin reduces the risk of certain cancers, such as stomach cancer and colorectal cancer. According to research, the anti-cancer properties of these allium vegetables are related to the sulfur compounds and flavonoid antioxidants, which can inhibit tumor growth and slow down the spread of cancer cells.

Special precautions

People with sensitive stomachs
Onions are pungent vegetables and are rich in fructo-oligosaccharides, which can cause bloating easily. People with sensitive stomachs should avoid eating raw onions.

Side effects

There are no known side effects of the consumption of onions.



There are no known allergies of the consumption of onions.

How to eat it?

White onions
They can be eaten raw, slow-cooked or baked.


Yellow onions
They are more juicy, sweet, and the flesh is more tender. They give a pungent odor when being cut open. They are suitable for stir-frying and soup.


Purple onions
They are less juicy, but the flesh is more crunchy. It is the spiciest amongst all. They are suitable to be added to salads or as side dishes.

Nutritionist’s tips

Cooked onion vs raw onion – Which one is healthier?

Apart from the difference in taste, cooked and raw onions have different levels of nutritional benefits. Upon heating, some nutrients in onions may be broken down. For example, vitamin C in onions is heat-sensitive, and it can be easily destroyed by heat. Also, allicin in onions can only be released after being exposed to oxygen in air at room temperature.

Therefore, if you want to reduce the loss of nutrients on onions, it is recommended to shorten the cooking time or eat them raw, such as onions served with oil and vinegar, in salad, which can retain more nutrients.

Food Functions
Blood glucose regulation
Promote bone health
Nutrition Labels
Dietary Fibre
Vitamin C