Asparagus

Health Benefits
(Source: World's Healthiest Foods, George Mateljan)

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

  • 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

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 WHFoods! (This ratio—22 out of 29—is equal to 76%, meaning that asparagus can provide you with a concentrated amount of all but seven nutrients that we analyze on our website.)

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!

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 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.

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 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 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 kitchen, 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 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.

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.

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