It's been a month since I hung the onions I dug up in June under the eaves. Once their outer skins are dry enough to crackle, they're finally ready to store and eat through the winter. This is also the time of year to pull out the broccoli seed packets before sowing in August.
These two crops have something in common: quercetin, a yellow plant pigment. You'll also find it in apple skins, blueberries, and the white pith of mandarin oranges.
What Is Quercetin?
Plants make quercetin to protect themselves from UV rays and insects. For years, studies have reported that when people eat it, it helps lower oxidative stress in the body. In onions, most of it sits in the papery brown skin and the one or two layers just beneath it, not in the center. The part we peel off and throw away is where it's most concentrated.
The new study, published in a scientific journal, didn't look at quercetin itself. It looked at a version with a phosphate group attached, called quercetin-3-O-phosphate. This compound has been found in onions, apples, berries, broccoli, and citrus fruits.
What the Study Found, and What It Didn't Test
More than 2 million people worldwide are diagnosed with lung cancer every year. Smoking is the biggest risk factor, but air pollution and other environmental exposures play a role, as do genetic mutations. A common problem in treatment is drug resistance. Over time, cancer cells adapt to targeted drugs, and the drugs stop working.
The researchers thought a compound that acts on several targets at once might make resistance less of a problem. They chose seven proteins involved in lung cancer and used computer software to test known drug compounds against each one. The only compound that attached firmly to all seven was quercetin-3-O-phosphate. To check whether it would stay attached, they also ran long simulations that followed the molecule's movements over time. It barely moved out of position.
But all of this happened on a computer. The compound still has to be tested on cells, then in animals, then in people. The researchers themselves say the results need to be confirmed through experiments. This doesn't mean eating lots of onions will prevent lung cancer.
Taking It from the Garden to the Table
Gardeners can still take something useful from this. Most of the vegetables high in quercetin are ones we already grow, and small changes in how you cook them affect how much of it ends up on your plate.
- When you peel an onion, take off only the dry brown skin. Keep the purplish layer underneath and sauté it along with the rest.
- Steam broccoli for about 3 minutes instead of boiling it for a long time. That way, less of the quercetin dissolves into the water.
- Wash apples and eat them with the skin on. The skin holds more quercetin than the flesh.
- Your body absorbs quercetin better when you eat it with some fat. A spoonful of olive oil in the pan is enough.
You can also save onion skins and simmer them with your stock. The broth gets a deeper color, and you throw away less.
So far, this research has only been done on computers. Here's one thing you can do today: for dinner tonight, sauté an onion, and keep the layer just under the brown skin.
