Onions
not only provide flavor; they also provide health-promoting
phytochemicals as well as nutrients.
Onions
contain quercetin, a flavonoid (one category of antioxidant
compounds). Antioxidants are compounds that help delay or slow
the oxidative damage to cells and tissue of the body. Studies
have indicated that quercetin helps to eliminate free radicals
in the body, to inhibit low-density lipoprotein oxidation (an
important reaction in the atherosclerosis and coronary heart
disease), to protect and regenerate vitamin E (a powerful antioxidant)
and to inactivate the harmful effects of chelate metal ions.
Major
dietary sources of quercetin include tea, onions and apples.
Recent studies at Wageningen Agricultural University, the Netherlands,
showed that the absorption of quercetin from onions is twice
that from tea and more than three times that from apples. Based
on studies conducted at The Queen's University at Belfast, Ireland
and Wageningen Agricultural University, the content of quercetin
in onions is estimated to be between 22.40 mg and 51.82 mg per
medium-sized onion (100 gram). Further research at the Agricultural
University on Wageningen showed that daily consumption of onions
may result in increased accumulation of quercetin in the blood.
Studies are in progress to determine whether the increased quercetin
accumulation from eating onions translates into significant
antioxidant benefit.
Other
studies have shown that consumption of onions may be beneficial
for reduced risk of certain diseases. Consumption of onions
may prevent gastric ulcers by scavenging free radicals and by
preventing growth of the ulcer-forming microorganism, Heliobacter
pylori. University of Wisconsin-Madison researchers found that
the more pungent onions exhibit strong anti-platelet activity.
Platelet aggregation is associated with atherosclerosis, cardiovascular
disease, heart attack and stroke. A study in progress at the
University of Wisconsin is determining the extent to which onion
consumption and specific onion compounds affect the in vivo
aggregation of blood platelets. "Using an in vivo model,
we are beginning to investigate and, in some cases, confirm
the potency of the onion as a blood thinner and platelet inhibitor.
Onions may be among the vegetables that will be prized not only
for their addition to our cuisine, but for their value-added
health characteristics," said Irwin Goldman, Associate
Professor of Horticulture, University of Wisconsin-Madison.
A
recent study at the University of Bern in Switzerland showed
that consumption of 1 g dry onion per day for 4 weeks increased
bone mineral content in rats by more than 17% and mineral density
by more than 13% compared to animals fed a control diet. This
data suggests onion consumption has the potential to decrease
the incidences of osteoporosis.
Several
studies have shown quercetin to have beneficial effects against
many diseases and disorders including cataracts, cardiovascular
disease as well as cancer of the breast, colon, ovarian, gastric,
lung and bladder.
In
addition to quercetin, onions contain the phytochemicals known
as disulfides, trisulfides, cepaene, and vinyl dithiins. These
compounds have a variety of health-functional properties, including
anticancer and antimicrobial activities.
Onions
are also a source of vitamin C, potassium, dietary fiber and
folic acid. They also contain calcium, iron and have a high
protein quality (ratio of mg amino acid/gram protein). Onions
are low in sodium and contain no fat.
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