Onions are part of the allium family of vegetables and herbs, which also includes chives, garlic, scallions and leeks. Allium vegetables have been cultivated for centuries for not only their characteristic, pungent flavors but also for their medicinal properties.
Onions can vary in size, shape, color and flavor. The most common types are red, yellow and white onion. Flavors can vary from sweet and juicy with a mild flavor to sharp, spicy, and pungent, often depending on the season in which they are grown and consumed. It is estimated that 105 billion pounds of onions are harvested each year worldwide.
The possible health benefits of consuming onions include lowering the risk of several types of cancer, improving mood and maintaining the health of skin and hair.
This MNT Knowledge Center feature is part of a collection of articles on the health benefits of popular foods.
Nutritional breakdown of onions
Consuming onions could lower the risk of several types of cancer, improve mood and maintain the health of skin and hair.
Onions are a nutrient-dense food, meaning that while they are low in calories they are high in beneficial nutrients like vitamins, minerals and antioxidants. One cup of chopped onion contains approximately 64 calories, 15 grams of carbohydrate, 0 grams of fat, 0 grams of cholesterol, 3 grams of fiber, 7 grams of sugar, 2 grams of protein and 10% or more of the daily value for vitamin C, vitamin B-6 and manganese. Onions also contain small amounts of calcium, iron, folate, magnesium, phosphorus and potassium and the antioxidants quercetin and sulfur.
Possible health benefits of consuming onions
Consuming fruits and vegetables of all kinds has long been associated with a reduced risk of many lifestyle-related health conditions. Many studies have suggested that increasing consumption of plant foods like mangoes decreases the risk of obesity and overall mortality, diabetes, heart disease and promotes a healthy complexion and hair, increased energy, overall lower weight.
Cancer: Allium vegetables have been studied extensively in relation to cancer, especially stomach and colorectal cancers. Their beneficial and preventative effects are likely due in part to their rich organosulfur compounds. Although the exact mechanism by which these compounds inhibit cancer is unknown, possible hypothesis include the inhibition of tumor growth and mutagenesis and prevention of free radical formation.1
Onions are also a source of the strong antioxidant vitamin C that helps to combat the formation of free radicals known to cause cancer.
Colon cancer: High fiber intakes from all fruits and vegetables are associated with a lowered risk of colorectal cancer.
Prostate cancer: In a study published by the Journal of the National Cancer Institute, researchers used a population-based, case-controlled study to investigate the relationship between allium vegetable intake and prostate cancer. They found that men with the highest intake of allium vegetables had the lowest risk for prostate cancer.2
Esophageal and stomach cancer: Frequent intake of allium vegetables has been inversely related with the risk of esophageal and stomach cancer.3 Several survey-based human studies have demonstrated the potential protective effects of consuming alliums, as well as reports of tumor inhibition following administration of allium compounds in experimental animals.
Sleep and mood: Folate, found in onions, may help with depression by preventing an excess of homocysteine from forming in the body, which can prevent blood and other nutrients from reaching the brain. Excess homocysteine interferes with the production of the feel-good hormones serotonin, dopamine, and norepinephrine, which regulate not only mood, but also sleep and appetite as well.4
Skin and hair: Adequate intake of vitamin C is needed for the building and maintenance of collagen, which provides structure to skin and hair.
How to incorporate more onions into your diet
Onions can be sautéed, roasted, grilled or caramelized, be used fresh as a topping for sandwiches or salads and added to salsas and dips.
Look for onions that are dry and firm with little to no scent before they are peeled.
Adding onion is a great way to add flavor to a dish without adding extra calories, fat or sodium. They are often a staple in many kitchens and pair well with most dishes. They can be sautéed, roasted, grilled or caramelized, be used fresh as a topping for sandwiches or salads and added to salsas and dips.
Potential health risks of consuming onions
It is the total diet or overall eating pattern that is most important in disease prevention and achieving good health. It is best to eat a diet with variety than to concentrate on individual foods as the key to good health.
Written by: Megan Ware, RDN, LD, registered dietitian and nutritionist