Asparagus

Health Benefits

Asparagus Has A Nutritional Uniqueness that is Second to None

A former member of the lily family of plants, asparagus now has its own plant family named after it—the Asparagaceae family. This fact alone should tell you something about the uniqueness of this vegetable, a uniqueness that we believe has been fully earned.


Many people might associate this uniqueness with the unusual urine odor that can often be so quickly detected when asparagus is consumed. And while we will provide you with more information about this unique aspect of asparagus later in this section, for now let's focus on the nutritional uniqueness of this food. Researchers have identified nearly 100 phytonutrient compounds in asparagus, and you will find some of these spotlight compounds listed below.

• 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
• hinokiroresinol
• Amino Acids
• asparagine
• Phenolic acids
• vanillic acid
• caffeic acid
• coumaric acid
• ferulic acid
• Flavonoids
• apigenin
• noricaritin
• isorhamnetin
• kaempferol
• Other
• asparagus acid
• rhodioloside D

          Of course, not shown in the list above are more common flavonoids (like quercetin and rutin) as well as the "conventional" nutrients that we rank in our WHFoods rating system. For asparagus, excellent rankings go to 8 nutrients: vitamin K, folate, copper, vitamin B1, selenium, vitamin B2, vitamin C, and vitamin E; very good rankings go to 12 additional nutrients: fiber, manganese, phosphorus, vitamin B3, potassium, choline, vitamin A, zinc, iron, protein, vitamin B6, and pantothenic acid; and good rankings go to 2 additional nutrients: magnesium and calcium. In other words, not only does asparagus contain the unusual list of phytonutrients presented in the chart above, but it also ranks as a good, very good, or excellent source of 22 of the 29 nutrients that we rank at World Wide Foods! (This ratio—22 out of 29—is the same as 76%, meaning that asparagus can provide you with a concentrated amount of all but seven nutrients that we analyze.)


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, asparagus 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.


There is one further important point that we would like to make about the urine odor of asparagus and asparagusic acid. 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 Benefits of Asparagus

                    It's not surprising to see asparagus being heralded as an anti-inflammatory food because it provides a truly unique combination of anti-inflammatory nutrients. Among these anti-inflammatory nutrients are asparagus saponins, including asparanin A, sarsasapogenin, protodioscin, and diosgenin. One of these saponins (sarsasapogenin) has been of special interest in relationship to amyotrophic lateral sclerosis (ALS), also known as "Lou Gehrig's Disease." Even though ALS is classified as a chronic, neurodegenerative disease and is not currently accepted as an autoimmune disorder, excessive, unwanted inflammation may play an important role in the death of certain nerve cells (motor neurons) in ALS. 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.


            In the antioxidant category of health benefits provided by asparagus we would place glutathione (GSH) and rutin at the top of the list. GSH is one of the body's premiere antioxidant molecules, which consists of three amino acids—glutamic acid, cysteine, and glycine—linked together; GSH is known as a trippeptide 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 rich in one particular antioxidant flavonoid called rutin. Many of our WHFoods contain rutin—just not in the same amount as provided by asparagus. (Buckwheat would be an exception here as it is actually higher in this flavonoid.) Rutin has been especially interesting to researchers because of the special role it may play in Maillard reactions. In the kichen, Maillard reactions are familiar to us as the browning reactions that take place when the sugars in food react with amino acids. (The browning of bread when toasted is a good example here.) When rutin is present during the Maillard reaction process, it may become involved with the Maillard reaction products in such a way as to increase free radical scavenging and to lower risk of oxidative stress.


                       The overall antioxidant capacity of asparagus has recently been measured by researchers in Brazil. These researchers analyzed 23 commonly eaten vegetables in Brazil (including asparagus). Their overall results showed turmeric, watercress, lettuces, and broccoli to provide the greatest overall antioxidant capacity. However, in some of the vegetables testing, asparagus came out in the top 10 among all 23 vegetables for overall antioxidant capacity. This finding is not surprising, given the many conventional and unconventional antioxidants present in asparagus. It's worth remembering here that asparagus ranks as an excellent source of both vitamin E and vitamin C—two spotlight antioxidants—as well as the mineral selenium, which plays a key role in the function of glutathione peroxidase (one of the most-studied antioxidant enzymes in the body).


              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 show 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, it is still a quite concentrate 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: cancers, type 2 diabetes, and high blood pressure. In the area of cancers, 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 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.


                     We would emphasize that the vast majority of studies that we have seen in all three of these areas involve rats and mice provided with asparagus extracts rather than humans enjoying asparagus in their meal plans. Hopefully, future researchers will look at these same types of events in large-scale studies on human participants who include differing amounts of asparagus in their diets.

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.

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

        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. Asparagus is an excellent source of vitamin K, folate, copper, selenium, vitamin B1, vitamin B2, vitamin C, and vitamin E. It is a very good source of dietary fiber, manganese, phosphorus, vitamin B3, potassium, choline, vitamin A, zinc, iron, protein, vitamin B6, and pantothenic acid. Additionally, it is a good source of magnesium and calcium.

What's New and Beneficial about Asparagus

• In a recent food science study, researchers reached this exact same conclusion about the sensitivity of asparagus to cooking. The researchers examined the effect of water blanching (brief submersion in boiling water) on asparagus quality using varying experimental lengths of time between 50 seconds and 6 minutes. They also examined the impact on four different sections of the asparagus spears: the bud (or tip), the upper portion (just below the bud), the middle section of the spear, and the butt (or bottom of the spear). The study results showed that a minute difference in blanching time could have a significant impact on the asparagus, and that the tips were significantly more sensitive to the blanching process than the lower and thicker portions of the spears.

• 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.

• Quercetin is one of the best-researched flavonoids in nutrition, and its intake has been linked to reduced risk of numerous cardiovascular diseases as well as other chronic health problems. Headed up by onions. But not as familiar to many people is the role that asparagus plays as an outstanding source of this flavonoid. In a recent study of more than 500 residents near Hokkaido, Japan, asparagus turned out to be the most important dietary source of quercetin (following onions). In fact, while 41% of all dietary quercetin came from onions, 29% came from asparagus (which was well ahead of green tea, which came in third place at 8%). It's worth noting here that 20 different quercetin-containing foods were included in the study.

• 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

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.