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 (TSU) in
San Marcos and the University of Texas at Austin (UT) through the American
Botanical Council’s (ABC’s) Dietetic Internship Program, led by ABC Education
Coordinator Jenny Perez.
We would like to acknowledge Jenny 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 Courtney Thompsonb
a HerbalGram Assistant Editor b ABC Dietetics Intern (TSU, 2015)
History and
Traditional Use
Range and Habitat
Asparagus
(Asparagus officinalis, Asparagaceae)
is an herbaceous perennial with stalks that can grow to several feet in height.
Most asparagus is harvested once the stalk reaches 6-8 inches in height. The
stalk is the edible portion of the plant, along with its pointed, budlike tip.1,2
If asparagus is not harvested, the stalks grow into finely textured, fern-like
plants before going dormant in winter.3 In the United States, the
primary asparagus producers are the states of California, Washington, and
Michigan.4 Depending on the cultivation method, asparagus yields a crop in one of three colors:
green, white, or purple. Green asparagus, the most common in the US, is allowed
to grow exposed to sunlight until harvested. White asparagus contains no
chlorophyll due to human intervention, which involves mounding dirt on the
stalk as it grows to shield it from sunlight.1 Purple asparagus,
which contains anthocyanins, is allowed to grow only 1-2 inches above the soil
before it is cut.5 Depending on the climate, most asparagus plants
are harvested from late spring to early summer.1
Phytochemicals and Constituents
Asparagus is a nutrient-dense food with an abundance of vitamins and minerals and
a low amount of calories. One cup of asparagus contains approximately 27
calories.2 Compared to other vegetables, asparagus is lower in
carbohydrates and higher in protein.6
Asparagus
contains high amounts of amino acids, including aspartic acid and asparagine.
Aspartic acid helps counteract excess amounts of ammonia in the body, which can
cause fatigue and low energy.5 Asparagine, a diuretic, breaks down
oxalic and uric acid formations in the kidneys and muscles, so the byproducts
may be eliminated through urine.
Asparagus is a good source of vitamins A, C, and E, as well as other
antioxidant compounds, such as glutathione.3 Glutathione contains
sulfur atoms, and is partially responsible for the sulfurous smell that
asparagus releases during cooking. Glutathione, which the body naturally
produces, supports a healthy immune system and liver, particularly in cases of
chronic diseases, though research into these effects is ongoing.7,8
Plants in the genus Asparagus also
contain saponins.9 Saponins exhibit a number of different properties
in the human body, including antioxidant, immunostimulant, antihepatotoxic,
antibacterial, antidiabetic, cytotoxic, and antimicrobial. The saponins present
in asparagus lend a bitter characteristic to the plant’s taste and also
contribute to its diuretic properties.10 While these compounds often
have beneficial effects on humans, saponins from certain plant sources can be
toxic to animals (which usually consume different saponin-containing plants,
and in much higher quantities, than humans).
Historical and Commercial Uses
The genus Asparagus includes about
300 species. Native to northern Africa, Europe, and Asia, A. officinalis was first cultivated by the Egyptians, Greeks, and
Romans. Since ancient times, asparagus has had a famous following, recorded as
being offered to the gods of the ancient Egyptians,5 eaten by King
Louis XIV of France,1 and the favorite vegetable of US President
Thomas Jefferson.11 Since early cultivation, commercial asparagus is
grown in subtropical and temperate climates including in the US, Mexico, Peru,
France, Spain, and the Mediterranean region.2
Asparagus has been used traditionally for a variety of health benefits. In
Europe and Asia, asparagus has been used medicinally as a diuretic and laxative,
as well as a treatment for heart disease, hypertension, rheumatism, acne,
infertility, eye problems, and menstrual cramps.3,11 The ancient
Greeks and Romans used asparagus to alleviate pain from toothaches and bee
stings.5 They also believed asparagus would help prevent and remove
kidney stones by flushing out the kidneys.9 The phallic shape of
asparagus contributed to its widespread use as an aphrodisiac, which has
persisted well into modern times.12
Ayurvedic practitioners used asparagus species for their anti-inflammatory
properties, which are attributed to the saponin constituents.3 In
India, the root of shatavari (A. racemosus)
has been used traditionally to treat infertility and menstrual cramping, and as
a galactagogue (to stimulate breast milk production).9 Asparagus is
still consumed worldwide as a therapeutic food for its antifungal,
anti-inflammatory, and diuretic properties.13
Modern Research
Due to the many nutrients and bioactive compounds found in asparagus, researchers
are investigating the possible applications of the plant. While the majority of
research has been in vitro, using extracts from the asparagus stalk, there are
several promising preliminary animal studies using whole asparagus as the
intervention.
Asparagus has a long history of traditional use for the management of diabetes.
In one animal study, researchers compared the effectiveness of a methanolic
extract of asparagus to that of glibenclamide, a common prescription medication
for type 2 diabetes.14 The asparagus extract, when provided at 500
mg/kg daily for 28 days, was shown to be comparable to glibenclamide in
improving beta-cell function and insulin secretion. While the actual effects of
consuming the whole plant (asparagus) were not considered, the outcomes of this
study may suggest a more natural treatment option.
Hypertension (high blood pressure) is a growing problem in the US. High blood
pressure can lead to renal (kidney) and cardiovascular disease. To help reduce
the risk of hypertension, angiotensin-converting enzyme (ACE) inhibitors are
often prescribed to help dilate blood vessels. Asparagus contains
naturally-occurring ACE inhibitors.15 When hypertensive rats were
fed a diet of freeze-dried, chopped green asparagus, ACE activity was
significantly lower than in rats fed a normal diet. The asparagus accounted for
5% of the normal diet. This was the only in vivo study in which asparagus was
consumed as a whole food. Further research is necessary to compare effects of
consuming the whole food to the effects of using asparagus extracts.
A 2014 literature review summarizes the effects of asparagus extract on the
cardiovascular, urinary, and immune systems.6 Instead of using only
the stalk of the asparagus plant, this review examines extracts composed of all
parts of the asparagus plant, including the roots. This type of asparagus
extract reduced homocysteine, an amino acid that promotes thickening and
hardening of the arteries and increases the risk of atherosclerosis. Increased
amounts of B vitamins and folate have been shown to decrease homocysteine
levels, and because of the high levels of these nutrients in the whole-asparagus
extract, individuals experienced a 28% reduction in homocysteine levels after
four months of use.
Asparagus extract appears to support kidney health via diuretic properties,
increasing urinary output and lowering water retention. According to the same
2014 review, the use of asparagus extract normalized kidney function (lowering
levels of creatinine and urine protein, and lowering creatinine clearance) and
decreased the risk of kidney stones by helping flush out the system before
formation occurs.6 Finally, asparagus extract helped maintain and enhance immune function for immunocompromised
individuals.6 Radiation and chemotherapy patients took asparagus
extract in conjunction with their existing therapy regimens. Individuals who
supplemented with asparagus extract had higher immune responses and increased
rates of survival and quality of life compared to the control group. Cancer
patients who supplemented with asparagus extract extended their lives at least two
months during stage 3 and at least six months during stage 2. Further research
is necessary to evaluate the effectiveness of using asparagus extract compared
to the effectiveness of using the whole plant as complementary cancer treatments.
In addition to the possibility of alleviating the symptoms associated with many
chronic diseases, asparagus extract has been evaluated in vitro for its
potential to alleviate alcohol-induced hangovers.13 Using all parts
of the asparagus plant, a preparation was made to induce cellular metabolism of
ethanol. While the constituents of the asparagus stalk alone were effective in
increasing ethanol metabolism within the cells, the effect increased when the constituents
from the asparagus leaves were added, demonstrating whole-plant synergy. This
research highlights the potential hepatoprotective benefits of the asparagus
leaf, which is often discarded.
Researchers
evaluated six common cooking methods (baking, broiling, pan frying,
microwaving, grilling, and steaming) to determine which method of asparagus
preparation was the most effective for retaining the important antioxidants
glutathione and rutin.16 Glutathione concentrations significantly
increased (compared to the raw asparagus control) with short cooking times after
baking, microwaving, and steaming. However, decreased glutathione
concentrations were seen after baking (18 minutes), frying (14 minutes) or
grilling (three minutes) compared to controls. Boiling was the only cooking
method that had a negative effect on rutin concentrations: rutin levels
decreased after seven minutes of boiling.
Antioxidant activity was measured by three assays: total phenolic content
(TPC), ferric reducing/antioxidant power (FRAP), and oxygen radical antioxidant
capacity (ORAC).16 Boiling for at least 11 minutes and extended
periods of baking caused significant decreases in TPC activity. Steaming,
frying, and baking for seven minutes significantly increased the TPC in the
asparagus, while other cooking methods had no effect. For FRAP and ORAC
measurements, duration of cooking time did not significantly affect the results.
However, steaming, frying, baking, and microwaving significantly increased FRAP
activity, while baking and frying significantly increased ORAC measurements. All
other methods had no effect on antioxidant capabilities. This study suggests
that the beneficial properties of asparagus are not significantly affected when
cooked in short durations regardless of cooking method.
Few adverse reactions have been reported after asparagus consumption. Because
asparagus contains small amounts of oxalates, individuals with a history of oxalate-containing
kidney stones should avoid consuming large amounts of asparagus.2
Additionally, asparagus contains purines that can lead to increased discomfort
in individuals with gout. Asparagus also induces a unique side effect: a
distinctive smell in the consumer’s urine, first recorded in the 18th century
by John Arbuthnot, physician to Britain’s Queen Anne.11 Interestingly,
some individuals lack either the ability to produce the smell or detect the
smell, likely due to a single nucleotide polymorphism.17 For the
majority of people, however, asparagus is a safe and delicious addition to a
healthy diet.
Nutrient Profile18
Macronutrient Profile: (Per 1 cup [approx. 134 g] raw asparagus)
27 calories 3 g protein 5.2 g
carbohydrate 0.2 g
fat
Secondary Metabolites: (Per 1 cup [approx.
134 g] raw asparagus)
Excellent source of: Vitamin
K: 55.7 mcg (69.63% DV) Vitamin
A: 1013 IU (20.26% DV)
Very good source of: Folate:
70 mcg (17.5% DV) Iron:
2.87 mg (16% DV) Manganese:
0.28 mg (14% DV) Thiamin:
0.19 mg (12.67% DV) Vitamin
C: 7.5 mg (12.5% DV) Dietary
Fiber: 2.8 g (11.2% DV) Riboflavin:
0.19 mg (11.18% DV)
Good source of: Potassium:
271 mg (7.74% DV) Vitamin
E: 1.51 mg (7.5% DV) Phosphorus:
70 mg (7% DV) Niacin:
1.31 mg (6.55% DV) Vitamin
B6: 0.12 mg (6% DV)
Also provides: Magnesium:
19 mg (4.75% DV) Calcium:
32 mg (3.2% DV)
DV =
Daily Value as established by the US Food and Drug Administration, based on a
2,000 calorie diet.
Recipe: Asparagus,
Edamame, and Parsley Salad
Adapted from Better
Homes and Gardens19
Ingredients:
- 4
tablespoons avocado or olive oil, divided
- 2
tablespoons mirin (sweet rice wine)
- 1
tablespoon rice vinegar
- 1
tablespoon reduced-sodium soy sauce or tamari
- 1
teaspoon salt
- 1
clove garlic, minced
- 1
pound fresh asparagus spears, woody ends trimmed off
- 6
cups of lettuce, washed and torn
- 1
cup frozen, shelled edamame, thawed
- 1
cup parsley, coarsely chopped
Directions: - For dressing,
combine 1 tablespoon of oil with the mirin, rice vinegar, soy sauce, salt, and
garlic in a small bowl. Set aside.
- In a large skillet,
heat remaining oil over medium-high heat until shimmering. Add asparagus and
cook for 3-4 minutes, turning occasionally, until lightly browned and
crisp-tender.
- Transfer asparagus
to a large bowl. Add lettuce, edamame, and parsley. Drizzle in dressing to
taste and toss gently.
References
Van
Wyk B. Food Plants of the World: An Illustrated Guide. Portland, OR:
Timber Press; 2005.
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M, Pizzorno J, Pizzorno L. The Encyclopedia of Healing Foods. New York,
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Blumenthal M, Goldberg A, Brinkmann J, eds. Herbal Medicine: Expanded Commission E Monographs.
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Communications; 2000.
Naeve
L. Asparagus. Agriculture Marketing Resource Center website. August 2015.
Available here.
Accessed January 25, 2016.
Onstad
D. Whole Foods Companion: A Guide for
Adventurous Cooks, Curious Shoppers, and Lovers of Natural Foods. White
River Junction, VT: Chelsea Green Publishing; 2004.
Chi
TT. Asparagus extract for heart, kidney and immune functions. Nutritional Perspectives: Journal of the
Council on Nutrition. 2014;37(3):27.
Dröge
W, Breitkreutz R. Glutathione and immune function. Proc Nutr Soc. 2000;59(4):595-600.
Smith
R, Harbott E. Asparagus officinalis
(garden asparagus). Kew Royal Botanic Gardens website. Available here.
Accessed January 21, 2016.
Negi
JS, Singh P, Joshi GP, Rawat MS, and Bisht VK. Chemical constituents of Asparagus. Pharmacogn Rev. 2010;4(8):215–220.
Saponins.
Cornell University College of Agriculture and Life Sciences website. September
9, 2015. Available here.
Accessed January 25, 2016.
National
Geographic Society Staff. Edible: An
Illustrated Guide to the World’s Food Plants. Des Moines, IA: National
Geographic Society; 2008.
Yoest
H. Plants with Benefits. Pittsburgh,
PA: St. Lynn’s Press; 2014.
Kim
B, Cui Z, Lee S, et al. Effects of Asparagus
officinalis extracts on liver cell toxicity and ethanol metabolism. J Food Sci. 2009;74(7):H204-H208.
Hafizur
RM, Kabir N, Chishti S. Asparagus
officinalis extract controls blood glucose by improving insulin secretion
and ß-cell function in streptozotocin-induced type 2 diabetic rats. Br J Nutr. 2012;108(9):1586-1595.
Sanae
M, Yasuo A. Green asparagus (Asparagus
officinalis) prevented hypertension by an inhibitory effect on
angiotensin-converting enzyme activity in the kidney of spontaneously
hypertensive rats. J Agric Food Chem.
2013;61(23):5520-5525.
Drinkwater
JM, Tsao R, Liu R, Defelice C, Wolyn DJ. Effects of cooking on rutin and
glutathione concentrations and antioxidant activity of green asparagus (Asparagus officinalis) spears. Journal of Functional Foods.
2015;12:342-353.
Pelchat
ML, Bykowski C, Duke FF, Reed DR. Excretion and perception of a characteristic
odor in urine after asparagus ingestion: A psychophysical and genetic study. Chem Senses. 2011;36(1):9-17.
Basic
Report: 11011, Asparagus, raw. Agricultural Research Service, United States
Department of Agriculture website. Available here. Accessed January
20, 2016.
Asparagus,
Edamame, and Parsley Salad. Better Homes and Gardens website. Available here.
Accessed January 22, 2016.
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