Food as Medicine: Asparagus (Asparagus officinalis, Asparagaceae)
HerbalEGram: Volume 13, Issue 2, February 2016
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
aHerbalGram 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
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.
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)
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
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
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.
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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.
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Asparagus, Edamame, and Parsley Salad. Better Homes and Gardens website. Available here. Accessed January 22, 2016.