Editor’s Note: Each month, HerbalEGram highlights a conventional food and
briefly explores its history, traditional uses, nutritional profile, and modern
medicinal research. We also feature a nutritious recipe for an easy-to-prepare
dish with each article to encourage readers to experience the extensive
benefits of these whole foods. With this series, we hope our readers will gain
a new appreciation for the foods they see at the supermarket and frequently
include in their diets.
The basic materials for this series were compiled
by dietetic interns from Texas State University in San Marcos and the
University of Texas at Austin through the American Botanical Council’s (ABC’s)
Dietetic Internship Program, led by ABC Education Coordinator Jenny Perez. We would like to acknowledge Perez, ABC Special
Projects Director Gayle Engels, and ABC Chief Science Officer Stefan Gafner,
PhD, for their contributions to this project.
By Hannah
Baumana and Catherine Applegateb
a HerbalGram Associate Editor
b ABC Dietetics
Intern (TSU, 2016)
Overview
Shallot
(Allium cepa var. aggregatum, syn. A. ascalonicum, Amaryllidaceae)
is a variety of the common onion (A. cepa).1 Shallots grow natively in the
mountains of central Asian countries, including Afghanistan, Tajikistan,
Pakistan, and parts of Siberia and China, and they gradually spread throughout
Europe as international trade expanded.2 It is an herbaceous plant
with alternating foliar leaves that sheath at the base to create the
superficial impression that they originate from an above-ground stem.1 Shallot bulbs, which are bunched in
groups that resemble large garlic (A.
sativum) bulbs, are the portion of the plant commonly used.3 While
edible, the above-ground stems and leaves generally are discarded. France, the
Netherlands, Great Britain, and the United States are major commercial
producers of shallots, and many other countries throughout Southeast Asia and
Africa also cultivate and export them.1,2
Phytochemicals and Constituents
Of
all the onion varieties, shallots contain the highest amount of total
flavonols, which have been shown to reduce systemic inflammation and cellular
oxidation.4 Many of these bioactive components
have been isolated and studied in vitro for their potential protective effects
against chronic diseases such as cancer and diabetes.5 One such flavonol is quercetin,
which is one of the many phenolic compounds found in many fruits and vegetables
that exhibit biological activities.6 Quercetin is reportedly more
bioavailable from the dry skin of shallots rather than the flesh, where it is
mainly found in the form of quercetin glycosides (quercetin glycosides can be
broken down in the body to produce quercetin).7 When metabolized, quercetin forms
metabolites that are less biologically potent than quercetin glycosides, but these
metabolites still retain some anti-inflammatory properties that have been shown
to protect against inflammation-related diseases such as cardiovascular disease
(CVD).5
Antioxidants
are a group of bioactive compounds that, among other activities, reduce free
radical damage to lipids and DNA by reactive oxygen species (ROSs).
Antioxidants either accept or donate an electron to stabilize ROS and to reduce
their damaging capabilities. Phenolic compounds such as flavonols, carotenoids
(fat-soluble pigments that give some plants their orange, yellow, and red
colors), ascorbic acid (vitamin C), thiols, and tocopherols (vitamin E) are all
examples of antioxidant molecules.8
Flavonols
have been widely shown to have potent antioxidant activity in vitro and in
vivo. Flavonols have also been extensively studied for their actions on
inhibiting the proliferation of cancer cells in vitro. The antioxidant capacity
and the anti-proliferative ability of flavonols change depending on how these
compounds are metabolized. When tested in liver and colon cell lines designed
to mimic human metabolism, the antioxidant activity of the flavonols found in
shallots was retained more than the antioxidant activity of the flavonols found
in other onion varieties.8
Shallots
and other Allium crops have high
concentrations of organosulfides, which are sulfur-containing phytonutrients
that are metabolized by the enzyme alliinase when the plant tissue is ruptured (e.g.,
from cooking, chewing, or crushing).9,10 These compounds give Allium
plants their recognizable flavor and pungency, with different species differing
in flavor and pungency due to variations in the concentrations of types of organosulfides.9 Organosulfides are highly bioavailable in animal models, preserved
through metabolism, and can be detected in the blood at dose-dependent
concentrations.10 As a result, their antioxidant activity is retained. In humans, their
bioavailability is unknown, so further investigation is needed to determine
whether biologically active concentrations of organosulfides can be achieved
through traditional dietary intake or through pharmacological interventions.10
Finally, isoliquiritigenin is a flavonoid found in
high concentration in shallots. Like organosulfides, isoliquiritigenin is
highly bioavailable.11 Isoliquiritigenin absorption is dose-dependent and varies depending on tissue
type.
Historical and Commercial Uses
There
is little information regarding the historical medicinal uses of shallot, which
was originally named Allium ascalonicum
after its popularity in the city of Ascalon, Syria, but Allium crops generally were used to treat gastrointestinal issues
and tumors and known for their anti-microbial properties.12 The
Roman naturalist Pliny the Elder mentioned the shallot as one of six types of
onions known to the Greeks in his 77 CE encyclopedia Naturalis Historia.1 By 1554, shallots were grown in
Spain, Italy, France, and Germany and Baldassare Pisanelli, a 17th-century
doctor in Italy, described the shallot as “a delicious food that stimulates the
appetite when it is hot and makes tasty to drink.”4 Cultivation of shallots spread to
England from France by 1663, and shallots became a common crop in the United
States by 1806.1 Today, shallots are used for
culinary purposes: cooked in stews and soups, diced raw in salads or to
accompany meats, or pickled.1
Modern Research
There
are limited data regarding the effect of shallots as a whole food on disease,
but specific phytonutrients from shallot have been isolated and studied for
their activities and effects on different disease states.
Cancer Prevention
Plants
in the genus Allium, including
shallot, have been shown to significantly reduce the risk for gastric cancer in
humans. A meta-analysis of epidemiological studies showed that the consumption
of 20 grams daily of Allium
vegetables (equivalent to the weight of one garlic bulb) reduced the incidence
of gastric cancer in individuals when compared to those who consumed lower
amounts.13 Similarly, the World Cancer Research Fund (WCRF) in
conjunction with the American Institute for Cancer Research (AICR) published a
comprehensive report of the existing literature on diet and cancer that found
strong evidence to support shallot’s inhibiting effect on cancer cell lines.14
In addition to reducing the risk of gastric cancer, Allium vegetables were also credited with reducing the risk of all
cancers.14 However, the WCRF/AICR report recommended a higher dosage
of Allium vegetables (100 grams
daily) to reduce the risk for gastric and other cancers than that specified by the
previously mentioned meta-analysis.13,14
Individual
phytonutrients present in shallots have been studied for their capabilities to
inhibit the initiation, promotion, and progression of certain types of cancer. Isoliquiritigenin, for example, has been shown
to be a potent inhibitor of the metastatic potential of human prostate cancer
cells.15 This essentially results in the cell’s ability to “turn
off” growth in order to prevent the uncontrolled cell growth and division
important for tumor survival. Isoliquiritigenin has also been shown to induce
apoptosis (normal, pre-programmed cell death) via mitochondrial-mediated
effects.16,17
Similar apoptotic effects were observed when hepatoma, gastric, and melanoma
cancer cell lines were treated with isoliquiritigenin.16,17 In
addition, treatment with isoliquiritigenin in human lung cancer cells resulted
in cell cycle arrest, which inhibited cancer cell growth and proliferation.18
Studies that monitor in vivo effects of isoliquiritigenin are needed to further
explore the anti-tumor potential of this compound.
Isoliquiritigenin
has the potential to act as a safe alternative to commonly used chemotherapies.
In a mouse study, renal carcinoma was treated with isoliquiritigenin, which suppressed
pulmonary metastases without the
leukocytopenia and weight loss associated with administration of the commonly
used chemotherapy drug 5-fluorouracil.19 More
studies are needed to determine the dosage at which isoliquiritigenin is effective and safe in humans, but this phytochemical
may offer a promising alternative to approved chemotherapies that are
associated with harmful side effects.
Organosulfides
also contribute to the antioxidant activity of shallots.10 These compounds have been studied
in vitro for their ability to halt cell cycle progression, induce apoptosis,
and inhibit angiogenesis of tumor cells.10 Similar effects have been observed
in vivo, in which organosulfides have been linked to the inhibition of skin
carcinogenesis and prevention of both carcinogen-induced colon cancer and
carcinogen-induced esophageal tumors in rats.10 In a clinical trial involving the
administration of a high dose of metabolized organosulfides (200 mg per day)
over a five-year period, researchers observed a 22% lower incidence of all
cancers and a 47.3% lower incidence of gastric cancer in these individuals compared
to those who did not receive treatment.10 No adverse effects were observed
with this high-dose treatment, highlighting the safety of these compounds.
However, further research into the efficacy of these metabolites for cancer chemoprevention
is needed.
Diabetes
Shallot
as a whole food has been studied for its hypoglycemic activity. In a mouse study,
juiced shallot bulbs was administered orally.20 The blood glucose
levels of mice treated with shallot bulb juice were found to be 13.3% lower in
the treatment group, compared to an increase of 1.57% in the control group and
the end of the 15-day study period. Another animal study compared the
glucose-lowering effects of a shallot bulb extract and the commonly prescribed
blood glucose-lowering drug, metformin, in rats.21 The
reduction of blood glucose observed with shallot bulb extract treatment was
similar to that observed with metformin. In addition, treatment with the
shallot extract significantly inhibited the metabolism of ingested
carbohydrates and increased the cellular absorption of circulating blood
glucose.
Another
animal study compared the antioxidant and hypolipidemic properties of the
shallot bulb extract and metformin in diabetic rats.22 In
the group treated with the shallot bulb extract, the following increases in phase
II antioxidant enzyme activity were observed compared to the control group:
superoxide dismutase by 65%, glutathione peroxidase by 43%, and catalase by
55%. Metformin only slightly increased superoxide dismutase activity by 8% when
compared to the control group. When comparing lipid profiles, the shallot bulb
extract affected only very low-density lipoprotein (VLDL), which was reduced by
24% in comparison to the control group. Treatment with metformin was half as
effective, reducing VLDL by only 12%.
Anti-Inflammatory
A
high daily intake of flavonoids from fruits and vegetables is associated with
an approximately 50% reduction in mortality from CVD compared to consuming low
amounts.8 As quercetin is metabolized by the
human body, it retains the ability to function as an anti-inflammatory agent
and inhibits the expression of adhesion molecules on the surface of endothelial
cells.5 (The presence of adhesion molecules
on the surface of endothelial cells can contribute to vascular inflammation and
the formation of atherosclerotic lesions.5) By reducing these effects and by
reducing the damage caused by oxidative stress, flavonols can act as anti-inflammatory
agents to further reduce the risk for inflammatory-related diseases such as
certain types of cancer, diabetes, and CVD.23
Antimicrobial
Allium plants are
well-known for their disease resistance, which has been attributed in part to
the antimicrobial activity of saponins present within these plants.24 These
same properties have also been applied to human pathogens. Exposure of
antibiotic-resistant Mycobacterium
tuberculosis to shallot bulb extract resulted in bacterial death.25
Organosulfides have specifically been studied for their anti-fungal properties
against several genera of human pathogens including Candida, Cryptococcus, Trichophyton, Epidermophyton,
and Microsporum.12
Organosulfides have also been shown to be effective against many bacteria,
including Bacillus spp., Enterococcus spp., Escherichia coli, Helicobacter
pylori, Salmonella typhimurium, Staphylococcus aureus, and Vibrio
cholera. Organosulfides have synergistic effects when combined with
antibiotics and broad-spectrum fungicides.
Nutrient Profile26
Macronutrient Profile: (Per 1/4 cup
chopped shallot [approx. 40 grams])
29 calories
1 g protein
6.72
g carbohydrate
0 g fat
Secondary Metabolites: (Per 1/4 cup
chopped shallot [approx. 40 grams])
Good source of:
Vitamin
B-6: 0.14 mg (7% DV)
Manganese:
0.12 mg (6% DV)
Vitamin
C: 3.2 mg (5.3% DV)
Dietary
Fiber: 1.3 g (5.2% DV)
Also provides:
Potassium:
134 mg (3.8% DV)
Folate:
14 mcg (3.5% DV)
Iron:
0.5 mg (2.8% DV)
Phosphorus:
24 mg (2.4% DV)
Magnesium:
8 mg (2% DV)
Calcium:
15 mg (1.5% DV)
Thiamin:
0.02 mg (1.3% DV)
Trace amounts:
Riboflavin:
0.01 mg (0.6% DV)
Niacin:
0.08 mg (0.4% DV)
Vitamin
K: 0.3 mcg (0.4% DV)
Vitamin
A: 2 IU (0.04% DV)
Vitamin
E: 0.02 mg (0.01% DV)
DV =
Daily Value as established by the US Food and Drug Administration, based on a
2,000-calorie diet.
Recipe: Kumquat-Shallot
Vinaigrette
Courtesy of
Catherine Applegate
Ingredients:
- 1/3
cup extra virgin olive oil
- 1 tablespoon
champagne or white wine vinegar
- 1 tablespoon
brown or Dijon mustard
- 1 tablespoon
honey
- 1
small shallot, minced
- 5
kumquats
Directions:
- Combine
all ingredients except the kumquats in a jar or bowl.
- Grate
the zest from two kumquats into the dressing. Halve and seed all kumquats, leaving
the peel intact, and juice them into the dressing. Add the juiced kumquats into
the jar or bowl.
- Mix
all ingredients together with a whisk or by putting a lid on the jar and
shaking it vigorously.
- Refrigerate
in an airtight container for a few hours before use.
- Serve
dressing over a roasted beet or fresh green salad, or use as a sauce over
chicken, pork, or fish.
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