Members of the lily family, onions are a strongly flavored, highly aromatic, non-starchy vegetable that is used in almost every culture as a vegetable or for flavoring. According to the National Onion Association, onions are the third most consumed fresh vegetable in the United States and are available all year long.

Onions range in size from less than one inch in diameter to over 4.5 inches, and the bulbs can be yellow, red, or white in color. There are many varieties of onions that can be used in cooking. Even though it might not be your first choice, some may also be eaten raw.

Varieties range from the popular Spanish, Vidalia, yellow, white, red onion, cippolini, and pearl, and there are varieties such as scallions, shallots, and leeks. Their flavor ranges too—and can be mild, sweet, or spicy.

Onions are very low in calories and carbohydrate, which is a bonus because a little bit of onion goes a long way.

Nutrition Facts

The following nutrition information is provided by the USDA for one medium raw onion (110g) measuring approximately 2 1/2 inches in diameter.

Calories: 44
Fat: 0.1g
Sodium: 4mg
Carbohydrates: 10g
Fiber: 1.9g
Sugars: 4.7g
Protein: 1.2g

Carbs in Onions

One medium onion contains 10 grams of carbohydrates. Of these, 4.7 grams is sugar and 1.9 grams is fiber. It is a very low carb food and can be enjoyed in low carb and ketogenic diets. This makes onions a great ingredient to use in cooking for adding flavor and volume to meals.

Fats in Onions

On their own, onions are low in fat, less than 1 gram of fat per medium-sized vegetable. However, onions are typically prepared with fat, either sautéed in oil or butter, covered in salad dressing, or breaded and deep fried.

Protein in Onions

Onions are not a protein-rich food, with just a little over 1 gram of protein per serving.

Micronutrients in Onions

One medium onion contains 13 percent of your recommended daily needs of vitamin C and 4 percent of the daily potassium needs. It also contains folate and quercetin.

Health Benefits of Onions

Onions contain vitamin C, which is important in cell repair, including wound healing. The vitamin is also important in boosting immunity and has anti-aging properties.

Onions are also high in quercetin, a flavonoid that has antioxidant properties. Animal research and research using cell cultures have found that quercetin may help to protect against certain cancers by killing cancer cells. Notably, these types of studies can suggest possible helpful effects, but they do not provide proof that such effects can be achieved in humans. Preliminary studies also suggest that quercetin may help reduce the risk of heart disease.

Some studies have found that the consumption of onions may help to reduce the incidence of certain diseases, such as gastric ulcers by scavenging free radicals and preventing the growth of the ulcer-forming microorganism, Heliobacter pylori. However, the myth of putting an onion in a room to prevent the cold or flu is not true.

Common Questions About Onions

Why does cutting onions make me cry?

Onions can irritate the eyes due to sulfuric acid, which is produced and released during the cutting process. When you cut an onion you break cells, releasing their contents. Enzymes that were kept separate mix with the sulfenic acids to produce propanethial S-oxide, a sulfur compound that wafts upward toward your eyes, making them burn and tear. To reduce irritation, try wearing goggles or chilling the onion before slicing.

Will eating onions make me smell?

Onions contain sulfurous compounds that can be absorbed into the bloodstream when ingested and can escape from our pores when sweating. Therefore, some people may "smell like onions" after eating them. Onions can sometimes make your breath smell too, especially raw onions. To get rid of onion breath, try eating some parsley.

How many calories do onion rings have?

The nutrition profile of onion rings will vary based on the size of the onion ring and the quantity served. To give a baseline, a small serving of onion rings from a fast food restaurant is about: 320 calories, 16 grams fat, 41 grams carbohydrate, 840 mg of sodium, and 3 grams of protein.

Onion Recipes and Preparation Tips

Choose onions that do not have any cuts, bruises, or blemishes. When purchasing whole peeled onions, select ones with an outside layer that does not appear to be dehydrated. If you are purchasing fresh, pre-cut onions, make sure to use them before the expiration date.

Onions can be stored for quite a while if kept in proper conditions. Store dry bulb onions in a cool, dry, dark place with plenty of air movement. Do not store them in plastic, as lack of ventilation will reduce their storage life.

Refrigerate whole onions only when you are trying to extend the shelf life of sweet or mild onion varieties. Place them in a low humidity setting because they must be kept dry.

If you cut your onions and don't plan to use them all, store them in a sealed container for up to seven days. Pre-cut onions should be kept refrigerated and used before the expiration date.

Use onions to flavor sauce, stews, chili, or soup. Top whole grain sandwiches, wraps, or burgers with a slice of onion or dice up some raw, grilled, or sautéed onions and put them in your salads, side dishes, or eggs.

Try to avoid deep frying your onions or consuming onion rings, blooming onions, etc. as these types of food are high in calories, sodium, and unhealthy fat.

Here are some onion recipes to try:

Allergies and Interactions

Onion allergies are rare, but symptoms may include itching, hives, or swelling in the mouth and throat. In some rare cases, an allergic reaction to onions may cause more severe symptoms including anaphylaxis.

People who are following a low FODMAP diet should avoid onions, as they may cause abdominal pain, bloating, and gas.

Onions are generally safe, but in large amounts can have interactions with certain medications. They can have a diuretic effect, and act similarly to a water pill. In large doses, onions can also lower blood sugar in people taking anti-diabetic drugs and may interfere with anticoagulant and antiplatelet drugs.