Note: In some countries, spring onions are often confused with scallions, another variety of onions. While spring onions have a bulging bulb at the end, scallions have bulbs of the same width as the stems. The latter is also milder in taste compared to the prior.
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Different varieties of onions have different phenolic content, sugar composition, moisture, flavour and amount of antioxidants. A study says that the colour of different fruits or vegetables is dependent on a plant pigment called anthocyanins.
Red onions have more anthocyanins compared to spring onions and shallots. Also, chopping, oven roasting, refrigeration and frying do not significantly decrease the antioxidants and anthocyanins content in this onion type. 
On the other hand, another study has shown that the bulbs of spring onions are packed with many bioactive compounds that possess anti-inflammatory, analgesic, antioxidants, anti-diabetic and immunoprotective properties. 
Shallots have anti-Helicobacter pylori potential effect or say, the ability to ward off a bacteria type known as Helicobacter pylori which are responsible for stomach infection, gastritis and stomach cancer. Besides, shallots are packed with saponins, flavonols and sulfur species that may help prevent the growth of cancerous cells. 
What Are The Similarities?
All the three; spring onions, shallots and red onions belong to genus Allium and family Amaryllidaceae. A study says that the vegetables of this family may help prevent the risk of multiple cancers such as oesophagal cancer, prostate cancer and gastric cancer. They also exhibit cardioprotective, blood pressuring-lowering and anti-diabetic effects. 
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Spring onions, shallots, red onions are all nutritious and may help protect against a wide range of diseases. They all contain phenolic compounds, however, some have more and some less depending on the type and place where they are grown. Also, the difference in their taste, flavour and cooking methods allow them to be used as per the choice of dishes.
Onions are one of the oldest cultivated vegetables used for multiple purposes, apart from culinary. Well, sometimes, onions can confuse us when it comes to their shapes, sizes and colours.
Several onion species are found across the world and are recognised by different names depending on the country, state and market. You will be surprised to know that there are around 21 different types of onions and each of them plays a significant role in different cuisines like soups, gravies, curries and salads.
From all the 21 varieties, the three widely consumed onion varieties are spring onions, shallots and red onions. In this article, we will discuss the difference between the three of them and other details. Take a look.
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