Asparagus

What’s new and beneficial about asparagus

• A food science study testing water blanching times from 50 seconds to 6 minutes across four spear sections (bud, upper, middle, butt) found that even small differences in blanching time significantly affected nutrient retention and texture. The tips were far more sensitive to heat than the lower, thicker portions. Thin spears benefit from reduced cooking times (3 minutes versus 5 for a sauté).
• Recent research has underscored the value of careful storage of fresh asparagus. The key scientific finding here involves respiration rate. Like all vegetables, asparagus doesn’t instantly “die” when it is picked, but instead, continues to engage in metabolic activity. This metabolic activity includes intake of oxygen, the breaking down of starches and sugars, and the releasing of carbon dioxide. The speed at which these processes occur is typically referred to as “respiration rate.” Compared to most other vegetables, asparagus has a very high respiration rate. At 105 milligrams of carbon dioxide release per 6 minutes per 100 grams of food (at a refrigerator temperature of 41°F/5°C), this rate is about five times greater than the rate for onions and potatoes (stored at a room temperature of 68°F/20°C), and about three times greater than the rate for leaf lettuce and ripe avocado (stored at a refrigerator temperature of 41°F/5°C) . Asparagus’ very high respiration rate makes it more perishable than its fellow vegetables, and also much more likely to lose water, wrinkle, and harden. By wrapping the ends of the asparagus in a damp paper or cloth towel, you can help offset asparagus’ very high respiration rate during refrigerator storage. Along with this helpful step, we recommend that you consume asparagus within approximately 48 hours of purchase.
• In a dietary survey of over 500 residents near Hokkaido, Japan, asparagus ranked as the second-largest source of quercetin after onions. Of total dietary quercetin intake across 20 foods, 41% came from onions, 29% from asparagus, and 8% from green tea. Quercetin is a flavonol associated with reduced cardiovascular disease risk in multiple cohort studies.
• A unique group of phytonutrients called steroidal saponins has long been of special interest in asparagus. Because these saponins contain a steroid (fat-soluble) component and a sugar (water-soluble) component, they can have unique impacts throughout the body, including in the function of cell membranes and numerous aspects of immune response. Originally, the saponins in asparagus were of interest to food scientists because of their relationship to the bitter taste of this raw vegetable. (Reflecting the most recent research, it is the monodesmocidic saponins that are most closely linked to this bitterness.) However, scientists soon discovered that numerous saponins in asparagus—including asparanin A—have the ability to alter immune-system signaling processes as well as the development of certain cancer-related processes. Research in this area is largely still limited to studies on mice and rats, but the ability of asparagus extracts to inhibit the production of certain inflammation system signaling molecules (cytokines) including IL-6 (interleukin-6) and TNF (tumor necrosis factor) is helping to explain how asparagus extracts might be able to help reduce excessive inflammatory processes. Similarly, the ability of asparagus extracts to stimulate the activity of IL-12 (another cytokine molecule that helps certain white blood cells—called CD4+ T cells—differentiate into Th1 or T helper cells) may help explain some of the immunosupportive properties of this vegetable.

Recommendations

Our outstanding level of green vegetable intake at WHF is 8 servings of green vegetables per day. A variety of days in our WHF Meal Plan provide this outstanding amount, without compromising the delicious balance of textures and flavors in our World’ Healthiest Foods Meal Plan Recipes. The many different types of green vegetables available to provide you with exceptional nourishment are nothing short of astonishing! Not only can you choose from dark green leafy vegetables from the cruciferous group (for example, mustard greens, turnip greens, kale, or collards), but you can also choose from the leguminous vegetable group (like green beans or green peas), the squash/gourd group (including zucchini and cucumber), the parsley/umbelliferous group (like fennel and celery), green allium vegetables like leeks, green lettuces like romaine, and finally, of course, the asparagus group that includes asparagus. Rather than relying exclusively on any one of these green vegetable subgroups, we recommend that you consider including green vegetables across all of these subgroups when putting together your weekly meal plan.

Asparagus, cooked
1.00 cup
(180.00 grams)

Calories: 40
GI: very low

NutrientDRI/DV

 vitamin K101%

 folate67%

 copper33%

 vitamin B124%

 selenium20%

 vitamin B219%

 vitamin E18%

 vitamin C18%

 phosphorus14%

 fiber13%

 manganese12%

 vitamin B312%

 choline11%

 vitamin A10%

 zinc10%

 protein9%

 iron9%

 potassium9%

 pantothenic acid8%

 vitamin B68%

 magnesium6%

 calcium4%

Food Rating System Chart

• Health Benefits
• Description
• History
• How to Select and Store
• Tips for Preparing and Cooking
• How to Enjoy
• Individual Concerns
• Nutritional Profile
• References

Health benefits

Phytonutrient composition of asparagus

Asparagus belongs to the Asparagaceae family. Researchers have identified nearly 100 distinct phytonutrient compounds in this vegetable. Some of the most studied include:

• Organic acids
  • gluconic acid
  • malic acid
  • nonanedioic acid
• Oxylipins
  • dihydroxy-octadecanedioic acid
  • trihydroxy-octadecanedioic acid
  • hydroxyperoxy-octadecanedioic acid
• Saponins
  • asparanin A
  • protodioscin
  • sarsasapogenin
• Lignans/Norlignins
  • secoisolariciresinol
  • iso-agatharesinoside
• Amino Acids
  • asparagine
• Phenolic acids
  • vanillic acid
  • caffeic acid
  • coumaric acid
  • ferulic acid
• Flavonoids
  • apigenin
  • noricaritin
  • isorhamnetin
  • kaempferol
• Other
  • asparagus acid
  • rhodioloside D

Beyond these phytonutrients, one cup (180g) of cooked asparagus provides concentrated amounts of conventional nutrients: vitamin K (101% DV), folate (67% DV), copper (33% DV), vitamin B1 (24% DV), selenium (20% DV), vitamin B2 (19% DV), vitamin C (18% DV), and vitamin E (18% DV), along with meaningful amounts of 14 additional vitamins and minerals, all in just 40 calories.

One of the unique phytonutrients in asparagus listed in the chart above is asparagusic acid. Asparagusic acid is the compound responsible for the urine odor that many people associated with asparagus. In chemical terms, asparagusic acid (1,2-dithiolane-4-carboxylic acid) is unusually reactive due to the two sulfur atoms that are positioned adjacent to each other in the molecule. Among other things, this increased reactivity helps asparagusic acid break down rapidly and its derivatives are what researchers believe we smell after asparagus has been consumed. However, it’s important to note that people differ in three basic ways in terms of asparagus consumption and urine odor. First, there are differences in digestion while asparagus is inside our GI tract and differences in the absorption of asparagusic acid. Second, there are differences in the way we metabolize asparagusic acid if it gets absorbed up into our bloodsteam. And finally, there are differences in our ability to detect the presence of asparagusic acid derivatives. These factors can combine in such a way as to produce some unusual results. For example, one person might end up with significant amounts of asparagusic acid derivatives in his or her urine, but be unable to detect the odor, even when another person can!

Asparagusic acid also has structural significance beyond odor. This molecule has as its core component a sulfur-containing structure called 1,2-dithiolane. We have included asparagusic acid as a key nutrient in asparagus and we have placed this content about asparagus odor within our Health Benefits section because 1,2-dithiolane is a key structure for the formation of a key sulfur-containing organic acid and antioxidant called alpha-lipoic acid. In fact, it is the presence of 1,2-dithiolane that allows alpha-lipoic acid to participate as a cofactor in the enzyme activities of pyruvate dehydrogenase and alpha-ketoglutarate dehydrogenase. Both of these enzymes and their activities help provide a critical doorway into the pathways of aerobic metabolism, which requires special antioxidant protection. While researchers do not yet have a complete picture of asparagusic acid in terms of its antioxdant function, the presence of 1,2-dithiolane in its structure suggests that this function will be involved in a major way.

Anti-inflammatory and antioxidant compounds

Asparagus contains a distinct combination of anti-inflammatory phytonutrients. Among these are asparagus saponins, including asparanin A, sarsasapogenin, protodioscin, and diosgenin. One of these saponins (sarsasapogenin) has undergone some preliminary study related to amyotrophic lateral sclerosis (ALS), also known as “Lou Gehrig’s Disease.” Though this study has not been terribly successful, it speaks to the potency of this phytonutrient that researchers showed such a keen interest. In this anti-inflammatory context, it is worth noting that recent research on the shatavarins in asparagus (shatavarin I, II, III, and IV) has revealed another group of saponins that influence inflammation through cytokine messaging. These asparagus saponins are able to inhibit production of cytokines IL-6 (interleukin-6) and TNF (tumor necrosis factor) and in this way help reduce excessive inflammatory processes.

Among the antioxidant compounds in asparagus, glutathione (GSH) and rutin stand out. GSH is one of the body’s primary antioxidant molecules, which consists of three amino acids—glutamic acid, cysteine, and glycine—linked together; GSH is known as a tripeptide because it composed of three amino acids. GSH is so important as an antioxidant that its depletion within our cells is sometimes used to measure overall oxidative stress. GSH also plays a critical role in phase 2 of our body’s detoxification processes. Most of the profiled foods that we include on our website do not contain freely available, preformed GSH—but asparagus is one of the foods that does.

Asparagus is also concentrated in rutin, a flavonoid glycoside (buckwheat is among the few vegetables with higher rutin content). Rutin may interact with Maillard reaction products (the browning compounds formed when sugars react with amino acids during cooking) to increase free radical scavenging activity.

In a Brazilian study analyzing 23 common vegetables, asparagus placed in the top 10 for overall antioxidant capacity. This is consistent with its content of vitamin E (18% DV), vitamin C (18% DV), and selenium (20% DV per cup cooked), the last of which is a cofactor for glutathione peroxidase.

The polysaccharides in asparagus are also important to include in this section on antioxidant and anti-inflammatory health benefits. Polysaccharides are a very common type of complex carbohydrates, and you will sometimes hear them being referred to simply as “starches.” Most of the polysaccharides analyzed in asparagus to date involve the inulins and heteroxylans. These two large families of polysaccharides are not as common in foods, especially in concentrated amounts. In animal studies, the polysaccharides in asparagus have been shown to have both antioxidant and antitumor properties. With respect to the inulins, it is also worth noting here that while asparagus is not quite as rich in these polysaccharides as chicory root or Jerusalem artichoke, they are still a quite concentrated source.

Other health benefits of asparagus

There is a considerable amount of animal research (involving almost exclusively rats and mice) involving asparagus extracts and the development of three types of chronic disease: cancer prevention, type 2 diabetes, and high blood pressure. With regard to cancer prevention, most of the research has focused on the antioxidant and anti-inflammatory properties of asparagus extracts, even though some of the compounds in these extracts have been found to have direct antitumor properties in cell cultures. In the area of type 2 diabetes, the focus has been on better overall functioning of the beta cells of the pancreas that produce insulin—typically leading to better insulin secretion and better regulation of blood sugar. In the area of high blood pressure, one particular compound in the asparagus extracts—called 2’-dihydroxynicotianamine—has been shown to inhibit the function of an enzyme called angiotensin-converting enzyme (ACE). Because ACE activity results in a constricting of our blood vessels (including our arterial blood vessels), inhibition of ACE can help prevent this constriction. By preventing blood vessel constriction, the blood vessels keep a wider diameter and there is less pressure on our blood.

The vast majority of studies in all three areas involve rodent models given asparagus extracts rather than human dietary trials. Large-scale human studies examining different levels of asparagus intake are still needed.

Description

A former member of the lily (Lilaceae) family, asparagus has fairly recently been assigned a unique family of plants bears its name—the Asparagaceae family. Many plants in this family are non-edible—and in fact, so are many varieties of asparagus itself. However, there are some very welcomed exceptions here and one of these exceptions is what we simply called “garden asparagus” (Asparagus officinalis).

When you find asparagus in the grocery, what you are looking at are the spears (also called “stalks” or “shoots”) of the plant. These spears are produced by the crown of the plant, which is a consolidated uppermost portion of the roots. When asparagus is grown commercially, it is often the crowns that are planted.

At the tip of the asparagus spears you will notice a petal-shaped head. The asparagus tips are actually buds, and if the spears are left unharvested on the plant, these buds will open into a delicate and extensive fern-like structure. This fern-like structure is what allows the asparagus plants to capture sunlight, and store up enough carbohydrates in the crown to generate healthy new shoots. This fascinating growth cycle of asparagus has to be managed by asparagus farmers in such a way that the result is a multitude of delicious asparagus spears for us to enjoy.

The color naming of asparagus can be confusing. The asparagus that we typically find in the grocery store is green because the shoots of the plant have grown upward from the soil and into the sunlight, and they have used their chlorophyll pigments to gather energy from the sun. Most any of these green asparagus varieties can be transformed into white asparagus if the soil around the asparagus plants is gathered up into a mound that surrounds the growing shoots. The mound of soil surrounding the shoots will block the shoots from the sunlight and alter metabolic activities associated with the green chlorophyll pigments. So to a certain extent, “green asparagus” is a term that refers to the way in which the asparagus plants have been grown, with plenty of sunlight available for the growing shoots. And in just the same way, “white asparagus” is a term that refers to the way asparagus plants have been grown using mounds of soil to shield the growing shoots from the sun. However, over time, growers have developed specific varieties of asparagus, some of which thrive with their shoots in the sun and others that thrive with their shoots surrounded by soil. So it is possible to purchase asparagus seeds for green asparagus and for white asparagus as well, even though most of the green asparagus seeds could be grown to produce white asparagus if the soil mound technique was used.

In addition to green and white versions of asparagus are purple versions. These purple varieties have increased in popularity among some consumers of asparagus and you are likely to be seeing more of them in supermarkets. Anthocyanin pigments are responsible for the rich purple shades in these asparagus varieties (and anthocyanins themselves belong to the larger family of phytonutrients called flavonoids).

Popular varieties of green asparagus include Jersey Giant, Jersey Knight, and Mary Washington. Popular varieties of purple asparagus include Purple Passion, Sweet Purple, and Pacific Purple.

Before closing this Description section, it is important to note that wild asparagus (whose scientific genus/species is Asparagus racemosus), is a different species of asparagus than the asparagus (Asparagus officinalis) that you will find in the supermarket. Wild asparagus has a long history of use in plant medicines, including Ayurvedic medicine, which was originally developed in India over 5,000 years ago. In fact, a name often used for wild asparagus—Shatavari—comes from the Sanskit words “shat”—which is related to the “cent-” that we use in “century” to refer to the number 100—and “vari”—which is related to streams and the flow of water. In other words, this name for wild asparagus was chosen in a way that suggests “one hundred streams”—perhaps referring to the many different ways in which Shatavari could be used as a medicinal plant. Today, one active area of interest in wild asparagus involves the steroidal saponins found in this particular species of asparagus, appropriately named “shatavarins.”

History

Asparagus (including all its different species) is native to Africa, Asia, and Europe. Over time, it has also become adapted to and become naturalized in North America, South America, Australia and New Zealand. One species of asparagus, typically referred to as wild asparagus (Asparagus racemosus), played a special role in the development of Ayurvedic medicine in India, beginning over 5,000 years ago. Asparagus is presently cultivated in all parts of the world listed above.

At present, China is by far the largest commercial asparagus-producing country in the world with about 7 million metric tons of total production. Peru and Mexico are second and third in terms of global asparagus production, each with production in the range of 175,000-400,000 metric tons. Although U.S. per capita consumption of asparagus has somewhat increased in the last decade, planted acreage in the U.S. has actually decreased, with additional supplies coming from Peru and Mexico, along with several other countries in Central and South America.

While California remains the largest asparagus-producing state within the United States (followed by Washington and Michigan), the total amount of California acreage planted with asparagus has decreased significantly over the past decade. This is in part related to issues involving the unique growth cycle of this plant and the non-guaranteed available of water needed for crop growth.

How to select and store

As noted above, in the store you will generally find asparagus that is green, white or has purple hues. Generally, you’ll most likely to find white asparagus in canned form, although you can also find it fresh in some select gourmet shops; it is usually more expensive than the green variety.

Asparagus stalks should be rounded, and neither fat nor twisted. Look for firm, thin stems with closed tips (the tips of the green and purple varieties should be deeply colored). The cut ends should not be too woody, although a little woodiness at the base prevents the stalk from drying out. Once trimmed and cooked, asparagus loses about half its total weight. Use asparagus within a day or two after purchasing for best flavor and texture.

At WHF, we encourage the purchase of certified organically grown foods, and asparagus is no exception. Repeated research studies on organic foods as a group show that your likelihood of exposure to contaminants such as pesticides and heavy metals can be greatly reduced through the purchased of certified organic foods, including asparagus. In many cases, you may be able to find a local organic grower who sells asparagus but has not applied for formal organic certification either through the U.S. Department of Agriculture (USDA) or through a state agency. (Examples of states offering state-certified organic foods include California, New York, Oregon, Vermont, and Washington.) However, if you are shopping in a large supermarket, your most reliable source of organically grown asparagus is very likely to be asparagus that display the USDA organic logo.

Store in the refrigerator with the ends wrapped in a damp paper towel.

Tips for preparing and cooking

Preparation

Thin asparagus does not require peeling. Asparagus with thick stems should be peeled because the stems are usually tough and stringy. Remove the tough outer skin of the bottom portion of the stem (not the tips) with a vegetable peeler. Wash asparagus under cold water to remove any sand or soil residues. It is best to cook asparagus whole.

Cooking for nutrient retention

Of all of the cooking methods we tried when cooking asparagus, our favorite is Healthy Sauté. Healthy Sauté—similar to Quick Steaming and Quick Boiling, our other recommended cooking methods—follows three basic cooking guidelines that are generally associated in food science research with improved nutrient retention. These three guidelines are: (1) minimal necessary heat exposure; (2) minimal necessary cooking duration; (3) minimal necessary food surface contact with cooking liquid.

To Healthy Sauté asparagus, heat 5 TBS of broth (vegetable or chicken) or water in a stainless steel skillet. Once bubbles begin to form add whole asparagus, cover, and Healthy Sauté for 5 minutes. Transfer to a bowl and toss with our Mediterranean Dressing. (See our 5-Minute Healthy Sautéed Asparagus recipe for details on how to prepare this dish.)

If you want to cut asparagus into small pieces, it is best to cut them after they are cooked. Asparagus can be served hot or cold.

How to enjoy

Serving ideas

• Add cold asparagus to your favorite salad.
• Toss freshly cooked pasta with asparagus, olive oil and your favorite pasta spices. We especially enjoy thyme, tarragon and rosemary.
• Chopped asparagus make a flavorful and colorful addition to omelets.
• Healthy saute asparagus with garlic, shiitake mushrooms and tofu or chicken for a complete meal.

Recipes that feature asparagus

• Garlic Shrimp Salad
• Mediterranean Pasta Salad
• Steamed Salmon and Asparagus with Mustard Dill Sauce
• Stir-Fried Seafood with Asparagus
• 15-Minute Healthy Sauteed Chicken & Asparagus
• 15-Minute Healthy Sauteed Asparagus and Tofu
• Miso Stir-Fry
• Primavera Verde
• 5-Minute Healthy Sauteed Asparagus
• Warm Asparagus Salad

Individual concerns

Contrary to popular belief, persons who experience a strong odor coming from their urine after eating asparagus are not in any danger from eating this vegetable. In fact, the key substance that is involved with the urine odor produced by asparagus is an antioxidant nutrient that can provide us with health benefits. The nutrient is asparagusic acid (which also goes by the chemical name 1,2-dithiolane-4-carboxylic acid). Because we consider the asparagusic acid in asparagus to be a provider of health benefits, we’ve provided you with much more detailed information about the urine odor from asparagus in our Health Benefits section of this profile. You will find this information toward the end of the first subsection within Health Benefits, which goes by the header, “Asparagus Has a Nutritional Uniqueness that is Second to None.”

Nutritional profile

One cup (180g) at 40 calories provides vitamin K (101% DV), folate (67% DV), copper (33% DV), vitamin B1 (24% DV), selenium (20% DV), vitamin B2 (19% DV), vitamin C (18% DV), vitamin E (18% DV), phosphorus (14% DV), fiber (13% DV), tryptophan (12.5% DV), vitamin B3 (12% DV), manganese (12% DV), choline (11% DV), vitamin A (10% DV), zinc (10% DV). Additional nutrients include iron (9% DV), protein (9% DV), potassium (9% DV), molybdenum (8.9% DV), vitamin B6 (8% DV), pantothenic acid (8% DV), magnesium (6% DV), calcium (4% DV), among others. Asparagus contains a unique array of phytonutrients. Like chicory root and Jerusalem artichoke, it is an important source of the digestive support nutrient, inulin. Its anti-inflammatory saponins include asparanin A, sarsasapogenin, protodioscin, and diosgenin,. Flavonoids in asparagus include quercetin, rutin, kaempferol, and isorhamnetin. In the case of purple asparagus, anthocyanins are also among asparagus’ unique phytonutrients. You will also find unique lignans, norlignans, oxylipins, and phenolic aids in this vegetable.