Reviewed by Christine Mikstas, RD, LD on September 29, 2021
All kinds are considered a good source of this nutrient. Vitamin C helps your body heal and form blood vessels and other parts of the body. It’s also an antioxidant that fights free radicals. Those are molecules your body makes that can sometimes trigger damage. Experts recommend 90 milligrams of vitamin C a day. That’s the Daily Value, or the amount of a nutrient you should try to get every day. One average-sized onion has 9% to 18% of your Daily Value.
Onions have two kinds of fiber: dietary and prebiotic. One cup has 12% of the 21-38 grams you need every day. Fiber helps you feel full longer and have regular bowel movements. And when you feel full, you’re less likely to eat as much. That helps lower your risk of obesity. The prebiotic fiber in onions feeds your gut bacteria (probiotics) so they can grow.
All onions have quercetin, a flavonoid or antioxidant compound. Quercetin has anti-inflammatory properties, helps your body make vitamin E, and protects it from many forms of cancer. Every onion has antioxidants, but red and yellow ones have more than white onions.
One medium onion has about 8% of your recommended Daily Value. Vitamin B6 helps your body form red blood cells. It also breaks down protein and can be helpful to women with PMS and morning sickness.
Raw Is Healthiest
You’ll get the most benefit from onions if you eat them raw. Dice and toss them in salads, omelets, or guacamole. Or add them sliced to sandwiches. You can lightly sauté onions to soften them a bit without losing too much of the good stuff. Cooked onions aren’t bad for you -- they just don’t have as many nutrients.
Make Quick Pickled Red Onion
Slice a red onion and toss it in red wine vinegar and a pinch of salt. Let sit for 15 minutes, tossing every 5 minutes to coat. Top hot dogs, burgers, salads, or tacos with it for extra texture and tang.
Fill Your Fajitas
Lightly sauté sliced onion, bell pepper, and your choice of protein in oil and a few dashes of low-sodium soy or Worcestershire sauce. Serve in corn tortillas or over brown rice with salsa, sour cream, and guacamole. Bonus: Add raw onion to your guacamole.
The Soak Method
Onions contain a compound that can make your eyes water. Most of it is in the root. If raw onions are too strong for you, chop and soak them in cold water or chill them for 30 minutes to lessen their intense bite. And don’t cut into the root.
Store whole onions in a cool, dry, and well-ventilated place, not your refrigerator. Once you cut or peel one, you can keep it in the fridge for 7-10 days. But keep them away from potatoes -- onions make them sprout.
How to Choose Onions
Look for a firm one with no soft spots and dry outer skin. It should feel heavy in your hand and have no smell.
Stave Off the Stench
Still smell onions on your hands long after dinner’s over? Rub them with lemon juice.
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Danielle Fineberg, MS, RD, Jersey City, NJ.
FoodData Central: “Onions, raw.”
FDA: “Daily Value on the New Nutrition and Supplement Facts Labels.”
Institute of Medicine. Dietary Reference Intakes for Calcium and Vitamin D, National Academies Press, 2011.
Mount Sinai: “Quercetin.”
Mayo Clinic: “Chart of high fiber foods,” “Vitamin B6,” “Vitamin C.”
National Onion Association: “Pickled Red Onion,” “FAQs,” “How to Store An Onion,” “Tips,” “Did You Know?”