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Onions belong to the Allium family of plants, which also includes chives, garlic, and leeks. These vegetables have characteristic pungent flavors and some medicinal properties.

Onions vary in size, shape, color, and flavor. The most common types are red, yellow, and white onions. The taste of these vegetables can range from sweet and juicy to sharp, spicy, and pungent, often depending on the season in which people grow and consume them.

Farmers have cultivated allium vegetables for centuries. According to the Food and Agriculture Organization of the United Nations, China is the biggest producer of onions worldwide.

It is common knowledge that chopping onions causes watery eyes. However, onions may also provide potential health benefits. These may include reducing the risk of several types of cancer, improving mood, and maintaining skin and hair health.

In this article, we discuss the possible benefits of onions, their nutritional content, and how to include more of them in the diet.

Onions might have positive effects on several different aspects of health.

Cancer prevention

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The antioxidants in onions may help counter free radical compounds.

Researchers have examined allium vegetables extensively in relation to cancer, especially stomach and colorectal cancers.

A 2019 study in the Asia Pacific Journal of Clinical Oncology compared 833 people with colorectal cancer with 833 people who did not have the disease.

The researchers found that the risk of colorectal cancer was 79% lower in those who regularly consumed allium vegetables, such as onions.

Experts do not fully understand the exact mechanism by which some compounds in onions inhibit cancer. Some hypothesize that onions inhibit tumor growth and cell mutation.

One cup of chopped onions also provides at least 13.11% of an adult's recommended daily intake of vitamin C. As an antioxidant, this vitamin helps counter the formation of free radical compounds that have links to cancer.

One review from 2015 found a general relationship between an increased consumption of allium vegetables and a reduced risk of cancer, especially cancers of the stomach and gastrointestinal tract.

The authors note that there are compounds called organosulfurs in onions, some of which suppressed aspects of tumor growth. However, they conclude that not all organosulfurs have antioxidant properties.

Further research is necessary to confirm which compounds in onion have protective effects against cancer.

The review also highlighted gaps in the research to date. The authors suggested that onions and other allium vegetables do not prevent cancer in isolation but work in tandem with other lifestyle factors to reduce the risk.

They also advised that while research has revealed some associations between allium vegetable consumption and reduced cancer risk, the amount that a person needs to consume to get the maximum benefit is not yet clear.

Skin and hair

As a good source of vitamin C, onions may support the building and maintenance of collagen.

Collagen provides structure to skin and hair.

Blood pressure moderation

A 2019 review found that quercetin, a compound in onion skin, had links to lower blood pressure when the researchers extracted it and administered it as a supplement.

However, the study did not examine the potential effects on blood pressure of eating onion as part of the diet rather than taking quercetin in supplement form.

Onions are a nutrient-dense food, meaning that they are high in vitamins, minerals, and antioxidants while being low in calories.

One cup of chopped onion provides:

  • 64 calories
  • 14.9 grams (g) of carbohydrate
  • 0.16 g of fat
  • 0 g of cholesterol
  • 2.72 g of fiber
  • 6.78 g of sugar
  • 1.76 g of protein

Onions are a good source of the following nutrients, according to the recommended daily allowance (RDA) and adequate intake (AI) values from the Dietary Guidelines for Americans:

NutrientPercentage of daily requirement in adults
Vitamin C (RDA)13.11% for males and 15.73% for females
Vitamin B-6 (RDA)11.29–14.77%, depending on age
Manganese (AI)8.96% for males and 11.44% for females

Onions also contain small amounts of:

Onions pose few risks to the people who eat them.

However, some people may have an allergy or intolerance to onions. Anyone who experiences a reaction after eating them should be sure to seek medical attention.

Read more about the symptoms of food allergies here.

Onions have a reputation for making people cry during the cutting or chopping process. This response occurs due to the presence of a gas called syn-Propanethial-S-oxide.

This chemical is a compound liquid that acts as a lachrymatory agent, meaning that it causes tears or stings the eyes.

To reduce tears during chopping, the National Onion Association recommend chilling an onion for 30 minutes then cutting off its top. The person should then peel the outer layer of the onion and leave the root intact, as this part has the highest concentration of lachrymatory agents.

Despite the tears that they can produce, onions can be a healthful addition to any eating plan. However, a person's overall eating pattern is most important in disease prevention and good health.

Here, learn more about the link between onions and tears.

When selecting onions, people should look for those that are dry and firm with little or no scent before peeling.

Including onion in a dish is a great way to boost the flavor without adding calories, fat, or sodium.

Onions are a staple in many kitchens and complement most dishes. People can use raw chopped onion in a sandwich filling or as a salad topping. This vegetable also makes a tasty addition to salsas and dips.

Healthful recipes that include onions as a primary ingredient include:

They also taste great when people sautee, roast, grill, or caramelize them.

Although onions make a great addition to a balanced, healthful diet, people should eat a variety of foods rather than concentrating on individual options.

A selection of onions and onion products is available for purchase online.

Q:

Are spring onions as nutritious as regular onions?

A:

They are similar in their nutritional content, but spring onions contain more plant-derived antioxidants than bulb onions as the leafy green part of the plant is more extensive.

Spring onions also contain B vitamins and many minerals, including copper, iron, manganese, and calcium. In addition, the leafy green part of the plant is a good source of folic acid.

However, as people tend to use spring onions as condiments and in smaller quantities than bulb onions, the nutrient intake is generally less.

Miho Hatanaka, RDN, LD Answers represent the opinions of our medical experts. All content is strictly informational and should not be considered medical advice.