Onion Health Benefits, Risks, Tips

Onions are members of the allium plant family, which also includes garlic, leeks, and shallots. Onions are divided into two categories: spring onions, which have a mild flavor and whose green tops and bulbs are eaten; and globe onions, which have a more pungent flavor and dry outer skins that are discarded. Shallots possess features of both onions and garlic, but are milder. Red onions have a mild, somewhat sweet flavor, which makes them a favorite for salads and sandwiches. Stronger white and yellow varieties are ideal for cooking, because they become milder and sweeter upon heating and they also impart a pleasant flavor to other foods.

Although onions in general are not high in vitamins and minerals, the green tops of spring onions are a good source of vitamin C and beta-carotene. A cup of boiled onions provides about 225 mg of potassium. They are rich in phytochemicals like flavonoids which protect against disease.

Health Benefits

Protects against lung cancer.
A study published in the Journal of the National Cancer Institute reported on the significant correlation between the high intake of dietary flavonoids and a reduced risk of lung cancer. Foods with the flavonoids that offer the best protection include onions as well as apples and white grapefruit.

Fends off other types of cancer.
Sulfur compounds and flavonoids in onions may block the cancer-causing potential of some carcinogens. One Chinese study found that men who ate at least 1 Tbsp day of chopped onions and other related vegetables (garlic, scallions, chives, and leeks) had about half the risk of developing prostate cancer compared to men who ate less than ¼ Tbsp (4 mL) of these vegetables daily.

Prevents heart attacks.
Folk healers have long recommended onions as a heart tonic: Researchers have now documented that adenosine, an aspirin-like substance in onions, hinders dangerous clot formation that causes heart attacks.

May boost “good” cholesterol levels.
Studies indicate that onions may protect against the artery-clogging damage of cholesterol by raising the levels of the protective high-density lipoproteins (HDLs).

Stabilizes blood sugar levels.
In one Egyptian study of diabetic rats, onion juice reduced blood sugar levels by an amazing 70%. One of few published studies in humans, from India, dates back some 30 years, but it found that people with diabetes who ate 2 oz (57 g) of onions a day experienced a significant drop in blood sugar levels. Researchers credit these effects to the sulfur compounds in onions as well as their flavonoids. Furthermore, onions are one of the richest food sources of chromium, a trace mineral that improves the body’s ability to respond to insulin.

May stop skin infections.
Onions contain substances that have a mild antibacterial effect, which may validate the old folk remedy of rubbing a raw onion on a cut to prevent infection. However, more research is necessary.

Health Risks

Bloating and gas.
Onions contain fructose, a common sugar that causes gas. Although it may cause discomfort, gas and bloating is usually not harmful.

Eating Tips
• Make a sliced red onion, goat cheese, lettuce, and pumpernickel sandwich.
• Sprinkle raw minced sweet onion on bean dishes.
• Splash caramelized pearl onions with sherry vinegar as a condiment for roasts.

QUICK TIP:
Eat them raw
Cooking onions at a high heat significantly reduces the benefits of diallyl sulfide, their cancer-protective phytochemical. Fresh raw onion offers the most health benefits, and mincing (or even chewing) the onion helps to release its phytochemical power. 20% lower risk of heart disease was observed in people who ate the most onions along with other foods rich in flavonoids.

Buying Tips
• Globe onions should be firm, with crackly, dry skin. Reject any that feel soft, have black spots, which indicate mold, or have green sprouts showing at the top—these are well past their prime. They should have a mild odor. A strong, oniony smell indicates decay.
• Scallions, or green onions, should have crisp, dark green tops and firm white bottoms. In general, the ones with more slender bottoms will have a sweeter taste.

Storing Tips
• Globe onions should be stored in a cool, dry place away from direct light, which can give them a bitter taste. Do not store them near potatoes, which give off moisture and a gas that causes onions to spoil more quickly.
• Store scallions in the refrigerator. They can be kept for several days, but use them as quickly as possible before they begin to soften.