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Boost Cancer-Fighting Effects Of Onions And Garlic

Green beans with Brazil nut-garlic paste. Credit: Harriet Sugar Miller

Green beans with Brazil nut-garlic paste. Credit: Harriet Sugar Miller

Although some Buddhists may swear off onions and garlic because they allegedly arouse both anger and libido, these aromatics have powerful nourishing properties. Experts say you can enhance the many health-promoting and cancer-fighting effects of onions and garlic by adopting certain culinary habits. Are you ready to embrace the almighty bulbs?

I’ve been involved in a steamy love affair with onions ever since a Thai waitress admired my father’s long, droopy earlobes, a sure sign of longevity in her culture. Other than the hunks of salami he used to beg for at bedtime, what food do I most often associate with my dad? Why, onions, of course!

But what does real science have to say about onions and their garlic cousins? Like leeks, chives and scallions, the other “forbidden spices” of certain Buddhists and Hindus, onions and garlic are members of the allium family of vegetables, so named because they contain the enzyme allinase, which converts the sulfur-containing compound alliin to allicin, its active form.

Alliums have long been prized for their ability to lower cholesterol, blood sugar and pressure, to thin the blood and to attack microbes. Recent research shows they fight cancer, too.

Studies in human populations “suggest that allium vegetable intake reduces the risk of cancer,” writes Italian researcher Carlotta Galeone, “and laboratory investigations have provided convincing evidence that selected substances contained in garlic and other allium vegetables inhibit a variety of chemically induced tumours in animals,” including cancers of the breast, endometrium, colon and digestive tract.

Garlic and onions. Credit: Harriet Sugar Miller

Garlic and onions. Credit: Harriet Sugar Miller

The “selected substances” include those stinky, pungent, tear-inducing molecules of sulfur.

Imagine an insect biting into an allium’s leaf and getting sprayed. “Plant scientists believe that a plant’s chemical system develops as an evolutionary defense against pests,” said  Irwin Goldman, an onion expert and professor at the University of Wisconsin. Alliums originated in central Asia,  just north of Afghanistan — a rough neck of the woods, by any measure.

In addition to more than 50 variations on sulfur, onions have another trait going for them: They contain flavonoids, compounds that give plants color and contribute to a host of healthy benefits. Quercetin, which acts as an anti-inflammatory, antihistamine and antioxidant, is the most exalted. It’s also has been shown to inhibit estrogen.

Garlic breath and onion sense: Top 5 practices for using them

To maximize the health benefits of onions and garlic, Goldman said, you must adopt some simple culinary habits:

Tip 1: Attack alliums first, as soon as you get to the kitchen. 

By cutting onions and garlic, you break their cell walls, thus releasing those allinase enzymes.  To develop the full complement of sulfur compounds, you have to let the cut vegetables sit for a while so that the enzymes have time to go to work, Goldman said.

How long is that? Goldman suggested 30 minutes for onions while garlic researcher Suhasini Modem suggested about half that time for cloves of garlic. And sulfur expert Eric Block said shorter times may suffice. In other words, nobody knows for sure, so hedge your bets by choosing the least risky course of action.

You could even cut your onions and garlic far in advance,  Modem said, as long as you let them sit on the counter long enough, then refrigerate them to keep the sulfurs stable. Chopped garlic should last six to eight hours on the counter, she said, and two to three days in a cold fridge.

Tip 2: Don’t cut alliums too finely. 

If you do, the enzymes will undergo a short-lived reaction and quickly evaporate, Block said. (Crucifers cut too finely react the same way.)  But what if you desire a subtle mince? My solution is to keep the cut chunky at first, then cut the vegetables even more  just before you’re planning to consume them.

Tip 3: Choose small red and yellow onions grown in colder climates and peel them gently.

Pity the poor Vidalia. She may be southern and mellow, which could be attractive qualities in a mate, but the harsh northern varieties of onions grown in latitudes above 40 degrees are higher in healthy sulfurs, Goldman said. Red and yellow onions, including the small yellow-skinned shallots, also contain more flavonoids than other varieties while white onions appear to have the least.

Quercetin and other flavonoids concentrate in the outer layers of onions, so peel them slightly and throw the skins into soup stock or compost. Smaller onions are simply better value. Why pay for those hunks of flavonoid-free interiors?

Tip 4: Eat alliums raw or slightly cooked.

In the case of garlic, Modem found that cooking it — even a quick saute for two minutes — destroyed its ability to inhibit the growth of cancer cells. Other researchers, however, have found that cooking in the microwave for 60 seconds or even 45 minutes in the oven only partially destroyed garlic’s anti-cancer properties as long as it had time to percolate beforehand. Again, hedge your bets.

Sulfur compounds in all alliums do get destroyed by cooking, Goldman said, but the flavonoids in onions may get enhanced with slight exposure to heat. For that reason, he recommends raw or quickly sautéed onions, cooked for four to five minutes, max. 

Tip 5: Combine alliums with alliums and other healthy plant foods.

Even if you insist on cooking your alliums, you can increase their cancer-fighting qualities by throwing in some raw garlic, onions or their juices at the end. Combining garlic with olive oil, said Modem, may also add some anti-cancer synergy.  Some studies also suggest you can get a similar boost  by combining garlic  with tomatoes or with selenium. And if you’re really angling to hedge your bets, you could always snort those piercing fumes. Funny you should bring that up, Goldman said. High on his bucket list is a study of people who work in onion factories–and cry “sulfur” every day.

Green Beans With Brazil Nut-Garlic Paste

This recipe combines raw garlic with Brazil nuts, one of the few food sources of cancer-fighting selenium. Eaten together, the two may pack an even powerful anti-cancer punch.


2 cloves garlic, smashed and allowed to sit 15 minutes before using

5 Brazil nuts

2 tablespoons lemon juice

4 large handfuls raw green beans

Salt to taste


1. Grind garlic and nuts to make a paste.

2. Whisk in lemon juice.

3. Using a steamer and very little water, steam the green beans for a couple of minutes until bright green, then combine with paste.

Top photo: Green beans with Brazil nut-garlic paste. Credit: Harriet Sugar Miller

Zester Daily contributor Harriet Sugar Miller has been an independent health journalist and cancer survivor for two decades. She blogs about the nutrition-cancer connection at and is writing a book, with practical guidelines and easy recipes.

  • Harriet Sugar Miller 6·3·13

    Are you one of those people who gets heartburn from raw alliums? In some people, those alliums can cause the pyloric valve, the muscle between your stomach and small intestine, to open and close erratically. I’ve spoken to several people who say that ingesting chlorophyll solves the problem. Bring on the greens!

  • Dad Shelly 2·3·14

    Wow. Glad I decided to review old emails my daughter sent

    Great information Interesting to read to give onions and garlic time to rest

    So the smashing of garlic probably kills the cancer fighting benefits right

    Let me know fully cooking the onion or putting in a pot of soup that doesn’t give you good cancer fighting elements???

    Thanks for anybody’s reply

  • Harriet Sugar Miller 2·4·14

    Go ahead and smash that garlic, Dad Shelly! Smashing is good–It breaks down the cell walls, thus releasing the enzyme that activates the sulfur. Just give the garlic 10 to 15 minutes at rest before you use it. According to food scientist Irwin Goldman, cooking onions for more than 4 to 5 minutes will degrade the sulfur. One way to cook them quickly is to steam-saute. You saute them lightly in olive oil for a minutes or so, then add sauce, broth or just a tad of water, and cover and steam them for a couple of minutes. Let us know if that works for you.

  • Adelphia 4·24·14

    Not bad at all fellas and gallsa. Thanks.

  • Jess 12·28·14

    Incredibly informative, thank you! Looking to consume 5-6 cloves of garlic a day to help fight cancer cells. Am I reading right that once chopped (and has rested in the open air for 15/30 min +) the garlic can stay effective for 2-3 days in the fridge?

  • Harriet Sugar Miller 12·29·14

    Yes, Jess, you are reading that correctly. Chop garlic into chunks or even just smash it (you just need to break the cell walls to get the enzyme working), then wait around 15 minutes and stick it in the fridge for 2-3 days. That’s the advice of garlic researcher Suhasini Modem. Then, just before you’re ready to use the garlic, chop it even more finely.

    Nothing in science is certain, but thus far this seems to be the best practice for maximizing garlic’s cancer-fighting properties.

    Thanks for your comment.

  • Malinoma jackie 12·31·14

    Can I steam the crushed garlic for 30-45 secs before eating and still fight the cancer?

  • Harriet Sugar Miller 1·18·15

    I asked garlic researcher Suhasini Modem your question–and she says that she doesn’t know for sure. It might still fight the cancer if you steam it quickly, she says, but the research, to her knowledge, has not yet been done.

    Just curious…Why are you steaming the garlic?