Cry me a River: Onions and Your Health

Mireille Blacke, MA, RD, CD-N

Mireille Blacke gives you the skinny on what’s fit to eat in this monthly nutrition column. Click the veggies above for her archives.

Mireille Blacke gives you the skinny on what’s fit to eat in this monthly nutrition column. Click the veggies above for her archives.

“Life is like an onion: you peel it off one layer at a time, and sometimes you weep.”

Carl Sandburg, American historian, poet, and novelist (1878-1967)

“What? I can’t have layers?”

Cordelia Chase, “Buffy the Vampire Slayer,” Season 3, Episode 6 (1998)

Photo by Mireille Blacke

Think Global: White Onion. Photo by Mireille Blacke

Back in the late fall, my cousin Marcia emailed me to confirm or deny a rampant belief that leftover onions were toxic and/or poisonous. (You may have seen the email about “Ed, the chemist” that warned millions of others about the same subject.) Now that summer is in full swing and many of us are enjoying onions in our potato salad and atop our grilled burgers, this bit of food folklore seemed an appropriate topic for this column, especially since Registered Dietitians (RDs) are trained in Food Safety.

This myth about the onion and the circulated email are not based in scientific fact. Onions (raw or otherwise) are no more at risk for bacterial contamination or spoilage than any other vegetable. Therefore it is not the onion itself, but how the onion is handled that presents the food safety risk: Are your hands dirty? Are you using a dirty cutting board or knife? Those handling methods will certainly increase contamination risks, regardless of food choice.

It seems the onion (Allium cepa) has had its role in lore and legend for centuries. Part of the current misconception of the onion as a reservoir for bacteria is linked to its influence over the bubonic plague during the 1500s, when it was believed that an onion would absorb and protect against deadly infections. As far-fetched as this seems today, some of the onion’s lore as an antiseptic, antibacterial (antibiotic), and antiviral is rooted in truth.

Gerrit Dou's painting, Girl Chopping Onions, created about 1646, now in the Royal Collection, London

Gerrit Dou’s painting, Girl Chopping Onions, created about 1646, now in the Royal Collection, London

The facts? Research has shown that raw and cooked onions contain compounds called phenols and flavonoids that fight against inflammation, elevated cholesterol, cancer, free radicals, and complications from diabetes. Onions are a source of quercetin, an anti-inflammatory compound associated with beneficial effects on various forms of cancer, abnormal cholesterol levels, and heart disease. Flavonoids like quercetin have anti-allergic properties as well, and can help relieve asthma and hay fever by blocking some of the inflammatory responses in the airways. Quercetin is also associated with improved immune system functioning and reduction of complications from diabetes.

Consider the onion’s health properties as multi-layered, like its skin. In addition to quercetin, onions contain allicin, the organo-sulfur compound that helps to decrease the overall risk of stroke, peripheral vascular disease (PVD), and coronary artery disease (CAD) due to its ability to raise levels of HDL (beneficial) cholesterol and combat the formation of clogged arteries. (Read further for the connection between allicin and the onion’s tear-jerking capabilities.) Need more? Compounds in onions also help to build strong bones by inhibiting activity of osteoclasts (cells that break down bones) and increase calcium.

Antioxidant content varies between types of onion. [For example, shallots are packed with the highest antioxidant level, while Vidalia onions yield considerably less.] With a sweeter flavor than its white cousins, red onions are also host to potent antioxidants called anthocyanidins, the same flavonoids that give blueberries (link to their cognitive- boosting capabilities. A slice of red onion is mild enough to eat raw, so wedging it between tomato and your deli meat of choice will not only replicate a classic deli sandwich, but also add some health benefits to your lunch selection.

Onions sliced for a sandwich. By swatjester (Flickr) [CC-BY-SA-2.0 (], via Wikimedia Commons

Onions sliced for a sandwich. By swatjester (Flickr) [CC-BY-SA-2.0 (, via Wikimedia Commons

Onions are low in calories (just 40 calories per 3.5 oz. serving) and fats, but a good source of soluble dietary fiber. Onions can contribute their flavor to savory dishes without raising the caloric content to any great extent. In addition, they are low in sodium, and high in vitamin C, vitamin B6 and folic acid. Vitamin B6 in particular is influential on GABA levels in the brain, important in maintaining the balance between anxiety and calm. Onions are also a rich source of chromium, a trace mineral that helps to regulate insulin and blood sugar action, and can be helpful in diabetes management. Onions also contain the mineral manganese, which is associated with antioxidant and anti-inflammatory actions. Also, the sulfur-containing compounds in onions may benefit persons with coronary heart disease as sulfides lower blood lipids and blood pressure.

So why the tears? Sulfur is concentrated within an onion’s tissues as pyruvate, a negative ion of pyruvic acid, a naturally occurring acid found in foods. When an onion is cut, enzymes at the cut area get to work on pyruvate to produce allicin, a sulfur-containing compound. The more cutting, the more allicin is produced and released. Allicin-bearing fumes meet the moisture film on our eyes and dissolve into it, producing sulfuric acid. Our eyes burn and our tear ducts start washing the irritant away. Typically, a simple splash of cool tap water on the eyes will stop the burning and the tears once started. To avoid future irritation, cut onions under running water or immersed in a basin of water. Refrigerating the onion before cutting will reduce the enzymatic reaction rate and also reduce irritation.

A little crying from onion-cutting pales in comparison for those people who suffer from allergic reactions after handling these vegetables. If you notice intense itching, runny nose, sweating, blurred vision, or asthma-like symptoms, seek medical attention immediately. An allergic reaction to onions can lead to anaphylaxis, a potentially fatal reaction including throat swelling, itchy rash, and low blood pressure. Often, cooked onions do not provoke the same intense reaction in individuals with raw onion allergies, because of protein denaturation during cooking.

Photo by Mireille Blacke

Photo by Mireille Blacke

Recommendations from this Registered Dietitian (RD):

  1. Get layered. Caramelized onions are an optimal low-calorie flavor builder and alternative to mayo and spreads. Caramelize a red onion until it’s sweet and moist, and amp up your grilled burgers this summer. Use as a condiment and sandwich topping. No, onion rings don’t count!

  2. Safety first. As with anything we consume, the need for Food Safety is consistent across all varieties of the onion family. This need increases when we consider that the onion is almost indispensable in cooking. The onion’s sugar content makes it useful in nearly all forms of cooking: baking, broiling, boiling, roasting, braising, frying, grilling, sautéing, steaming, or eating raw. Keep your Food Safety skills up-to-date.

  3. No more tears. To reduce eye irritation during onion slicing, cut onions under running water or submerged in a basin of water. Consider refrigerating the onion before cutting to slow the enzymatic reaction rate and also reduce irritation.

  4. Table the scraps. Onions can be toxic or deadly for pets and other animals. Do not feed your pets foods or leftovers containing onions, particularly pizza, onion     rings, many canned foods, or Chinese food. Be diligent about putting leftovers away promptly and not leaving them out for your pets to sneak a nibble or two.

  5. According to the Environmental Working Group, onions are one of the least-contaminated of pesticide-laden of fruits and vegetables.  With such a wide variety of onions to be enjoyed raw or cooked, it will save some pennies when you don’t have to buy organic to avoid foods heavily-sprayed with pesticides.

  6. Halitosis for health? Stronger tasting onions are associated with more superior health properties. For additional ways to excuse some of those pungent associations and more interesting information on onions, see the National Onion Association web site at

Onion lore has been rooted in both fact and fiction for centuries. Considering the onion brings tears to your eyes and also benefits your health, this contradiction makes some sense. While you can’t believe everything you read online, the onion’s health properties should not be similarly dismissed. Most people can improve their health profiles by adding raw or cooked onions to their dietary intake. Any way you slice it, that’s fine by me.


3 thoughts on “Cry me a River: Onions and Your Health

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