What's New and Beneficial About Onions
April 12, 2014
Story at-a-glance
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Onions are rich in sulfur-containing compounds and other
phytochemicals that may boost heart health, offer protection
against cancer and diabetes, boost bone health, and more
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Onions have a wealth of beneficial properties. They’re
anti-allergic, anti-histaminic, anti-inflammatory, and
antioxidant
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Onions have a particularly high concentration of beneficial
polyphenols, with more polyphenols than garlic, leeks,
tomatoes, carrots, and red bell pepper
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Wild onions have been enjoyed since the very early ages, and
were likely a staple in the prehistoric diet
By Dr. Mercola
If you’ve been eating an apple a day to keep the doctor away,
you would be wise to add an onion a day to that regimen. This
humble vegetable is a member of the Allium genus, making it
closely related to other superfoods like garlic, leeks,
scallions, and chives.
This means onions are rich in sulfur-containing compounds
that give them both their characteristic odor and much of their
health-boosting potential.
As one of the oldest cultivated plants, onions do not
disappoint in terms of nutrition. They’re a very good source of
vitamins C and B6, iron, folate, and potassium. But it’s their
phytochemicals – including the flavonoid quercetin and allyl
disulphide – that are most exciting to researchers.
To date, onions have shown a wealth of beneficial properties;
they’re anti-allergic, anti-histaminic, anti-inflammatory,
and antioxidant,1
all rolled into one. And if you take even a quick glance at the
available research, you’ll quickly understand why onions deserve
to make a very frequent appearance at your dinner table.
Onions Are Polyphenol Superstars
Polyphenols are plant compounds recognized for their
disease prevention, antioxidant, and anti-aging properties.
Onions
have a particularly high concentration, with more polyphenols
than garlic, leeks, tomatoes, carrots, and red bell peppers.2
In particular, onions are especially rich in polyphenol
flavonoids called quercetin. Quercetin is an antioxidant that
many believe prevent histamine release—making quercetin-rich
foods “natural antihistamines.” As reported by The World’s
Healthiest Foods:3
“…on an ounce-for-ounce basis, onions rank in the top
10 of commonly eaten vegetables in their quercetin content.
The flavonoid content of onions can vary widely, depending
on the exact variety and growing conditions.
Although the average onion is likely to contain less
than 100 milligrams of quercetin per 3-1/2 ounces, some
onions do provide this amount. And while 100 milligrams may
not sound like a lot, in the United States, moderate
vegetable eaters average only twice this amount for all
flavonoids (not just quercetin) from all vegetables per
day.”
Quercetin is available in supplement form, but there are a
couple of reasons why getting this flavonoid naturally from
onions makes more sense:4
- One animal study found that animals received greater
protection against oxidative stress when they consumed
yellow onion in their diet, as opposed to consuming
quercetin extracts.
- Quercetin is not degraded by low-heat cooking, such as
simmering. When preparing a soup with onions, the quercetin
will be transferred into the broth of the soup, making onion
soup an easy-to-make superfood.
Eating Onions May Lower Your Risk of Cancer
If you’re interested in using food to lower your risk of
cancer, eat onions. People who eat more onions, as well as other
allium vegetables, have a lower risk of many types of cancer,
including:5
- Prostate and breast
- Ovarian and endometrial
- Colorectal and gastric
- Esophageal and laryngeal
- Renal cell
Onions contain numerous anti-cancer compounds, including
quercetin, which has been shown to decrease cancer tumor
initiation as well as inhibit the proliferation of cultured
ovarian, breast, and colon cancer cells.6
As reported by the National Onion Association, onions are
considered a dietary anti-carcinogen:7
“The inhibitory effects of onion consumption on human
carcinoma have been widely researched… In a review on the
effects of quercetin… persons in the highest consumption
category versus the lowest had a 50% reduced risk of cancers
of the stomach and alimentary and respiratory tracts.
Organosulfur compounds [in onions] such as diallyl
disulfide (DDS), S-allylcysteine (SAC), and S-methylcysteine
(SMC) have been shown to inhibit colon and renal
carcinogenesis… Mechanisms of protection ranged from induced
cancer cell apoptosis and gene transcription inhibition to
protection against UV-induced immunosuppression.”
It’s unclear exactly how much onion consumption is necessary
for cancer protection, but research shows benefit from even
moderate consumption. Even one to seven servings of onions a
week may be protective, although some research suggests a daily
serving of onion (one-half cup) is best.
Heart Health: Are Onions Responsible for the French Paradox?
The so-called “French Paradox” -- the low incidence of heart
disease among the French, despite their relatively high-calorie
diet – has often been credited to the antioxidants in the red
wine they often consume.
But onions, which are very popular in French cuisine, may be
another contributing factor to their good health, particularly
heart health. The sulfur compounds in onions, for
instance, are thought to have anti-clotting properties, as well
as, improve blood lipid profiles. The allium and allyl
disulphide in onions have also been found to decrease blood
vessel stiffness by enhancing nitric oxide release.
This may reduce blood pressure, inhibit platelet clot
formation, and help decrease the risk of coronary artery
disease, peripheral vascular diseases, and stroke. The quercetin
in onions is also beneficial, offering both antioxidant and
anti-inflammatory properties that may boost heart health.
Onions Are Beneficial for Your Bones, Digestive Tract, Diabetes
Prevention, and More
The more we learn about onions, the more it becomes clear
that they offer whole body benefits. That is the beauty of
eating whole foods, after all, because they typically contain
many beneficial phytochemicals that enhance your health
in numerous synergistic ways. As for onions, research has shown
that including onions in your diet may offer the following
benefits:8
Prevent inflammatory processes associated with asthma |
Reduce symptoms associated with diabetes |
Lower levels of cholesterol and triglycerides |
Reduce symptoms associated with osteoporosis and improve
bone health |
Maintain gastrointestinal health by sustaining
beneficial bacteria |
Diminish replication of HIV |
Reduce risk of neurodegenerative disorders |
Lower your risk of cataract formation |
Antimicrobial properties that may help reduce the rate
of food-borne illness |
Improvement of intestinal flora, improved absorption of
calcium and magnesium due to the fructans they contain |
Antibacterial and antifungal properties |
Lower risk of certain cancers |
Onions Were a Prehistoric Staple Food
If there were any doubt as to how valuable onions have been
through the ages, it’s thought that wild onions have been
enjoyed since the very early ages, and were likely a staple in
the prehistoric diet. The National Onion Association stated:9
“Most researchers agree the onion has been cultivated
for 5,000 years or more. Since onions grew wild in various
regions, they were probably consumed for thousands of years
and domesticated simultaneously all over the world. Onions
may be one of the earliest cultivated crops because they
were less perishable than other foods of the time, were
transportable, were easy to grow, and could be grown in a
variety of soils and climates.
In addition, the onion was useful for sustaining
human life. Onions prevented thirst and could be dried and
preserved for later consumption when food might be scarce.
While the place and time of the onion’s origin is still a
mystery, many documents from very early times describe its
importance as a food and its use in art, medicine, and
mummification.”
Since ancient times, onions have been enjoyed around the
world for many uses:10
- The onion symbolized “eternity” to Egyptians, who would
bury them along with their Pharaohs
- In India, onions were valued as a diuretic and good for
digestion, the heart, the eyes, and the joints
- During the Middle Ages in Europe, onions were widely
consumed and prescribed medicinally for headaches,
snakebites, and hair loss
- Native American Indians used wild onions in cooking as
well as in poultices, dyes, and even as toys
Tips for Choosing and Preparing Onions
The average American eats about 20 pounds of onions a year,
which may sound like a lot until you learn that in Libya, which
has the highest onion consumption rate in the world, the average
person eats nearly 67 pounds a year.11
If learning about their health benefits has inspired you to eat
more onions, you’re in luck as they are incredibly versatile and
come in a variety of colors and flavors. The chart below, from
the National Onion Association,12
provides an excellent breakdown of which type of onion to use in
your cooking.
Color |
Variety or Type |
Availability |
Raw Flavor/Texture |
Best Usage |
Yellow Onion:
All-purpose and most popular, approximately 87 percent
of the U.S. onion crop is comprised of yellow varieties.
The most well-known sweet onions are yellow. The best
type of onion for caramelizing is a yellow storage
variety. Cooking brings out this variety's nutty,
mellow, often sweet, quality when caramelized. |
Sweet |
March-September |
Crisp, juicy, mild flavor with a slightly sweet ending
with little to no after-taste |
Raw, lightly cooked, sautéed, or grilled |
Fresh, Mild |
March - August |
Crisp, juicy, mild to slightly pungent with a faint
after-taste |
Raw, lightly cooked, sautéed, or grilled |
Storage |
August-May |
Strong onion flavor, mild after-taste |
Grilled, sautéed, caramelized, baked, or roasted |
Red Onion:
About eight percent of the U.S. onion crop is red. They
have gained popularity in the past decade, especially in
foodservice on salads and sandwiches because of their
color. |
Sweet |
March-September |
Crisp, very mild onion flavor |
Raw, grilled, or roasted |
Fresh, Mild |
March-September |
Bright tones, slightly less water content than yellow
with a slightly pungent ending |
Raw, grilled, or roasted |
Storage |
August-May |
Sharp, spicy, and moderate to very pungent |
Raw, grilled, or roasted |
White Onion:
Approximately five percent of U.S. onion
production is dedicated to white onions. They are
commonly used in white sauces, potato and pasta salads,
and in Mexican or Southwest cuisine. Due to the compact
nature of their cell structure, white onions do not
store quite as long as other varieties. |
Fresh, Mild |
March-August |
Moderately pungent and clean finish, very little
after-taste |
Raw, grilled, sautéed, or lightly cooked |
Storage |
August-May |
Moderately pungent to very pungent and full flavored,
but finishes with a cleaner and crisper flavor in
comparison to yellow and red storage varieties |
Raw, grilled, sautéed, or lightly cooked |
Source:
National Onion Association, All About Onions
A Trick to Avoid ‘Crying’ While You Cut Onions
Onions release a gas called lachrymatory factor (LF), which
causes tearing. Japanese researchers developed an onion that
lacked the enzyme necessary to produce LF, and therefore
wouldn’t cause tearing, but it also altered the beneficial
sulfur-containing compounds in the onion. So while the fact that
onions make you tear up is a bit inconvenient, it’s also a
reminder of the many potent health compounds they contain. That
being said, the World’s Healthiest Foods shared a few tips to
cutting onions that should help lessen eye irritation and
tearing. If this is an issue for you, don’t give up on onions.
Try these tips instead:13
“If cutting onions irritates your eyes, there are a
few tricks that you can employ. Use a very sharp knife and
always cut the onions while standing; that way your eyes
will be as far away as possible. Consider cutting onions by
an open window. If cutting onions really makes you cry,
consider wearing glasses or goggles.
Chill the onions for an hour or so before cutting;
this practice can slow down the onion's metabolism and
thereby lessen the rate of LF gas production. Cutting onions
under cold, running water is a method that is often used to
cut back on eye irritation, but it's a method we view as a
second-best choice since some of the nutrients found in
onion can be lost into the flow of water.”
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