Aspartic acid is a nonessential amino acid that is critical in the many complex metabolic processes associated with proteins. Although it is found in profusion in plant proteins, aspartic acid can also be manufactured in the body form oxaloacetic acid. Structurally, this amino acid (along with glutamic acid) is the only amino acid bearing a negatively charged carboxylate group on its side chain.
As various amino acids develop, aspartic acid is fundamental in the overall development and metabolism processes undertaken by these subunits of protein. Its main properties are principal in the construction of biochemicals in the citric acid cycle as well. Aspartic acid is responsible for the synthesis of both essential and nonessential amino acids, including; arginine, asparagine, isoleucine, lysine, methionine, threonine, and various nucleotides.
Aspartic acid remains a critical element in achieving and maintaining homeostasis and productivity in the mind and body.
Aspartic acid is categorized as a nonessential amino acid. When there are inadequate levels in the body, the liver maintains levels by creating the deficient amount. Due to this process, aspartic acid does not have to be solely obtained from diet.
Listed below are the sources that one might find in an average diet. The most bioavailable sources of aspartic acid include portions of dairy, beef, fish, poultry, and sprouting seeds. All food items listed below are based upon a 100 gram (200 Kcalorie) serving: 
|5790||Seaweed, spirulina, dried|
|5430||Seeds, cottonseed flour, low fat (glandless)|
|5350||Seeds, cottonseed meal, partially defatted (glandless)|
|5160||Seeds, sunflower seed flour, partially defatted|
|4650||Seeds, sesame flour, low-fat|
|4460||Seeds, cottonseed flour, partially defatted (glandless)|
|3980||Seeds, safflower seed meal, partially defatted|
|3740||Seeds, sesame flour, partially defatted|
|10200||Soy protein isolate|
|10200||Soy protein isolate, potassium type|
|10200||Soy protein isolate, potassium type, crude protein basis|
|7250||Soy protein concentrate, produced by acid wash|
|7250||Soy protein concentrate, crude protein basis (N x 6.25), produced by acid wash|
|6370||Peanut flour, defatted|
|5910||Soy flour, defatted|
|5910||Soy flour, defatted, crude protein basis (N x 6.25)|
|5850||Soy flour, low-fat|
|5850||Soy flour, low-fat, crude protein basis (N x 6.25)|
|5650||Soy meal, defatted, raw|
|5650||Soy meal, defatted, raw, crude protein basis (N x 6.25)|
|5300||Tofu, dried-frozen (koyadofu)|
|5300||Tofu, dried-frozen (koyadofu), prepared with calcium sulfate|
|4980||Soybeans, mature seeds, dry roasted|
|4590||Soybeans, mature seeds, raw|
|4430||Soybeans, mature seeds, roasted, salted|
|4430||Soybeans, mature seeds, roasted, no salt added|
|4370||Soy flour, full-fat, roasted|
|4370||Soy flour, full-fat, roasted, crude protein basis (N x 6.25)|
|4340||Soy flour, full-fat, raw|
|4340||Soy flour, full-fat, raw, crude protein basis (N x 6.25)|
|4120||Peanut flour, low fat|
|3880||Lupins, mature seeds, raw|
|6430||Fish, cod, Atlantic, dried and salted|
|5130||Mollusks, whelk, unspecified, cooked, moist heat|
|3630||Pork, cured, bacon, cooked, microwaved|
|8250||Egg, white, dried|
|6810||Egg, white, dried, flakes, glucose reduced|
|4760||Egg, whole, dried|
|4470||Snacks, pork skins, plain|
|4300||Snacks, pork skins, barbecue-flavor|
|5270||Gelatins, dry powder, unsweetened|
|3810||Gelatin desserts, dry mix, reduced calorie, with aspartame, added phosphorus, potassium, sodium, vitamin C|
|3810||Gelatin desserts, dry mix, reduced calorie, with aspartame, no added sodium|
Although aspartic acid is primarily used in the body’s metabolic processes; it is also key for a variety of other biological processes. Cellular energy is directly dependant upon this critical nonessential amino acid. This is a vital process in human physiology, and the responsibility for the increased stamina in neurological and muscular activities lies with sufficient levels of this amino acid. Chronic fatigue is a condition that may be directly linked to lower levels of aspartic acid. 
Inadequate levels of aspartic acid have also been linked to irregularities of certain chemicals in the brain, largely serotonin. The decreased levels of serotonin have been argued to be a primary contributor to depression in all age groupings. A proper balance insures proper functioning and balance of the brain and its associated processes.
L-aspartic acid has also been used in various clinical applications, showing promise in persons suffering from opiate addictions. A particular clinical study involved eight opiate addicted individuals; two were addicted to codeine, two to heroin, and four to opium. Clinical administration of 2 grams of L-aspartic acid, four times daily, took place for a two week period.  Clients showed a decrease in withdrawal symptoms and a greater improvement in social contact and overall behavior.
Aspartic acid is also significant in the removal of excess ammonia and other toxins from the bloodstream. It also assists in the proper functioning of carriers for genetic information - RNA and DNA. This amino acid is equally important in antibody synthesis/immune system support, production of immunoglobulin, cell-functioning, and the movement of minerals across intestinal linings into blood and cellular structures located throughout the body.
There has not been an established or recommended dosage for this particular amino acid. However, the U.S. National Academy of Sciences recommends that healthy people achieve .36 grams of highly bioavailable protein for each pound of bodyweight-equaling 0.8 grams of protein, per kilogram of bodyweight.
Aspartic Acid Deficiencies
There has been no evidence suggesting a deficiency of aspartic acid has taken place in human biology. Because aspartic acid is a nonessential amino acid, deficiencies are very unlikely to occur. Symptoms of deficiency have been speculated to produce fatigue, depression, autoimmune disorders, and ammonia toxicity in the body
Aspartic Acid Toxicities
The medical community does not focus exclusively on the amino acid aspartic acid itself, but places importance upon the substance which it produces - the artificial sweetener, aspartame. Aspartame is a dipeptide composed of the amino acids aspartic acid and phenylalanine. Upon human ingestion aspartame is quickly metabolized back into aspartic acid, phenylalanine, and also the toxic wood alcohol, methanol. Aside from the toxic properties of methanol, aspartic acid and phenylalanine are not completely benevolent. If one is not predisposed to ridding the body of both of these amino acids quickly, build-up can and may occur leading to alterations in brain chemistry.
Excessive consumption of both aspartic acid and phenylalanine leads to an increased level of these substances in the brain. Neurological damage may occur because of the over-stimulus of the cerebral cortex. The neurotransmitter serotonin may also be adversely affected due to over consumption of these two amino acids. Depletion of serotonin is often the case. This depletion can lead to conditions associated with such a disproportionate change in brain serotonin levels, including (but not limited to); fatigue, headaches, sleep/eating disorders, and in extreme cases, depression.
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2. Balch, Phyllis A., James F. “Amino Acids.” Prescription for Nutritional Healing. Ed. Amy C. Tecklenberg. New York, NY: Penguin Putnam Inc., 3rd Ed. 2000. 42-53.
3. H. Koyuncuoglu and others, “The antagonizing effect of aspartic acid on the brain levels of monoamines and free amino acids during the development of tolerance to and physical dependence on morphine [and opitates]”, Psychopharmacology, Vol. 54, 1977, pp. 187-191.
4. Zest for life information page. “RDA of amino acids.” (1999-2003) http://www.pdrhealth.com/drug_info/nmdrugprofiles/herbaldrugs/101840.shtml (14 Sept. 2004).