For starters, they contain dozens of types of antioxidants.
Get ready to cry some happy tears, because onions definitely deserve a spot on your cutting board this summer. White, yellow, red/purple, and green—all varieties of onions offer some pretty impressive health benefits. The veggie has long been held in high regard: Archeologists have uncovered traces of onions dating back to 5000 B.C. It’s said that in ancient Egypt, onions were worshipped because their shape and concentric circles symbolized eternity. And in the Middle Ages, onions were used to pay for goods and services, and given as gifts. It's no wonder when you consider just how good they are for you. Below, six excellent reasons to enjoy onions even more.
Onions are rich in antioxidants
They may not be overflowing with vitamins and minerals: One medium onion, which contains about 44 calories, provides 20% of your daily vitamin C needs, and between 5 and 10% of of the DV for B6, folate, potassium, and manganese. But onions are chock-full of antioxidants. They supply dozens of different types, including quercetin, a potent anti-inflammatory compound. The outer layers of an onion pack the greatest antioxidant punch.
They may protect against cancer
In a study published in the American Journal of Clinical Nutrition, researchers looked at how often people in Italy and Switzerland ate onions and another Allium vegetable, garlic. They found that among the populations studied, there was an inverse link between the frequency of use of these veggies and the risk of several common cancers—meaning the more onions and garlic people ate, the lower the cancer rate.
And improve bone density
One study that looked at perimenopausal and postmenopausal Caucasian women 50 and older found a link between onion consumption and bone health. Women who ate onions more frequently had better bone density, and decreased their risk of hip fracture by more than 20% compared to those who never ate onions.
Onions also support healthy digestion
That's because they're rich in inulin, a type of fiber that acts as a prebiotic. In a nutshell, prebiotics serve as food for probiotics, and help those beneficial microbes flourish. Inulin also helps prevent constipation, improve blood sugar regulation, boost nutrient absorption, and support healthy bone density. It's possible it can support weight loss too, by curbing appetite.
They may help lower cholesterol
One interesting study looked at overweight or obese women with polycystic ovary syndrome. In this randomized controlled clinical trial, the patients were assigned to either a high onion diet (consisting of raw red onion) or a low onion diet. After eight weeks, researchers found decreases in the cholesterol levels in both groups, but the drop was greater (including the reduction in "bad" LDL cholesterol) among the people eating a high onion diet. Another study tracked 24 women with mildly high cholesterol and found that those who drank onion juice daily for eight weeks had reductions in total cholesterol, LDL, and waist measurements compared to those who downed a placebo.
And onions make tomatoes better for you too
Food synergy is the idea that the benefits of eating two specific foods together outweigh the benefits of eating each food separately. That seems to be the case with onions and tomatoes: Scientists believe sulfur compounds in onions boost the absorption of lycopene, an antioxidant in tomatoes tied to protection against cancer and heart disease, as well as brain, bone, and eye health. Fortunately, tomatoes and onions make a delicious combination in omelets, salads, soups, and sautés.
How to reap the benefits of onions
Animal research suggests onions may also help control blood sugar levels, and support fertility. That means there will likely be more human studies to come on this superstar veggie. In the meantime, you'll do your body good by consuming a variety of types and colors, and eating them both raw and cooked.
If slicing onions makes your eyes water, here’s a tip: Cut them (safely) under running water or near a vent. This can help prevent some of the gas from making contact with your eyes. Or invest in a par of stylish kitchen goggles. And be sure to avoid touching your eyes after your onion prep!
Cynthia Sass, MPH, RD, is Health’s contributing nutrition editor, a New York Times best-selling author, and a consultant for the New York Yankees and Brooklyn Nets.