Phenylalanine is an aromatic amino acid that is classified as essential. From a nutritional standpoint, phenylalanine must be obtained (exclusively) from either dietary or supplementary sources. Adequate intake is critical, as it is responsible for tasks related to the central nervous system. This amino acid may impact the neurotransmitters responsible for mood, pain, appetite, and memory. 
Phenylalanine acts as a precursor to the amino acid tyrosine. The conversion of phenylalanine to tyrosine takes place by means of the enzyme L-phenylalanine hydroxylase. Upon this conversion, the body uses tyrosine to synthesize two critical neurotransmitters/catecholamines - dopamine and norepinephrine. Studies have shown that these two agents assist the body by improving organ perfustion, as well as oxygen delivery and consumption.  The release of both dopamine and norepinephrine by the adrenal glands is considerably increased in times of elevated stress; a subsequent process requiring adequate amounts of usable phenylalanine.
Phenylalanine exists in three different chemical forms; the L-, D-, and DL- forms. The L- (LPA) form is the most common form of phenylalanine. being the natural amino acid found in bodily proteins. The D- (DPA) form is the L- form’s mirror image and is synthesized in a laboratory. DL-phenylalanine (DLPA) is a 50:50 combination of the two previous forms. This is the most common form of phenylalanine used in dietary supplements because both forms wield specific physiological processes.
The majority of consumed phenylalanine results from ingesting protein rich food sources. Quality sources include; almonds, avocados, lima beans, peanuts, and seeds. Dietary considerations for the consumption of aspartame should also be taken into account. This dipeptide (L-phenylalanine and L-aspartic acid) is a popular alternative sweetener which provides ample amounts of phenylalanine. Serving sizes below are based upon 100 grams of a given food source and are expressed in milligrams, representing the amount of phenylalanine contained.
|1861||Leavening agents, yeast, baker’s, active dry|
|Vegetables and Vegetable Products|
|2777||Seaweed, spirulina, dried|
|Nut and Seed Products|
|3103||Seeds, cottonseed flour, low fat (glandless)|
|2658||Seeds, sesame flour, low-fat|
|2466||Seeds, sunflower seed flour, partially defatted|
|2138||Seeds, sesame flour, partially defatted|
|2031||Seeds, watermelon seed kernels, dried|
|2029||Seeds, cottonseed kernels, roasted (glandless)|
|1774||Seeds, safflower seed meal, partially defatted|
|Legumes and Legume Products|
|4594||Soy protein isolate|
|4594||Soy protein isolate, potassium type|
|3278||Soy protein concentrate|
|2705||Peanut flour, defatted|
|2453||Soy flour, defatted|
|2428||Soy flour, low-fat|
|2346||Soy meal, defatted, raw|
|2334||Tofu, dried-frozen (koyadofu)|
|2334||Tofu, dried-frozen (koyadofu), prepared with calcium sulfate|
|2066||Soybeans, mature seeds, dry roasted|
|1905||Soybeans, mature seeds, raw|
|1838||Soybeans, mature seeds, roasted, salted|
|1816||Soy flour, full-fat, roasted|
|1752||Peanut flour, low fat|
|Finfish and Shellfish Products|
|2452||Fish, cod, Atlantic, dried and salted|
|Dairy and Egg Products|
|4736||Egg, white, dried|
|2721||Egg, whole, dried, stabilized, glucose reduced|
|2515||Egg, whole, dried|
|2234||Cheese, parmesan, shredded|
|2081||Cheese, parmesan, grated|
|1922||Cheese, parmesan, hard|
Supplemental phenylalanine has shown great promise in numerous physical and cognitive disorders. Conditions such as arthritis, menstrual cramps, obesity, and migraines, are areas of ongoing study into the far-reaching benefits of phenylalanine supplementation. Clinical application of phenylalanine has garnered high opinion in the areas of chronic pain management, vitiligo, depression, and even Parkinson's disease.
Preliminary findings suggest that D-phenylalanine may be an effective antagonist against chronic pain.  Although findings vary in consistency, it is suggested that chronic pain associated with various health conditions is often reduced by supplemental D-phenylalanine. Phenylalanine may provide stimulation of certain neurological pathways in the brain that control pain. D-phenylalanine has also been shown to enhance pain relief when supplemented in combination with prescription pain medications.  This is a promising finding for the nearly fifty million Americans who suffer from persistent, or chronic, pain.
Vitiligo is a condition characterized by a pigmentation disorder in which white patches of skin appear on various parts of the body. Vitiligo destroys melanocytes (cells that make pigment), mucous membranes, and retina. Under medical supervision, UVA radiation in conjunction with oral and topical L-phenylalanine may darken (repigment) whitened areas of the body.  More research is necessary to determine the possible side effects of this treatment. 
The D- form of phenylalanine is metabolized within the body to phenylethylamine, or PEA. Phenylethylamine is a compound which occurs naturally within the brain, having a major influence on mood behavior. Inadequate or diminished urinary PEA levels are often found in depressed individuals. This characteristic is often symptomatic of a deficiency of phenylalanine.  Phenylalanine may help to stimulate areas of the brain responsible for dopamine and norepinephrine. Because D-phenylalanine alone is not common in supplements containing phenylalanine, the DL-form is often employed by those suffering from depression.
Phenylalanine’s most promising application may be in its symptomatic assistance with individuals suffering from Parkinson’s disease. This disease occurs when nearly 80% of the brain’s dopamine producing cells are damaged or have expired. Signs of Parkinson’s disease include; tremor, rigidity, slowness of movement, and difficulties keeping one’s balance. Parkinson’s disease affects nearly 1.5 million Americans, with 60,000 new cases being diagnosed each year. D-phenylalanine is often administered to Parkinsonian patients in conjunction with normal prescription medications. The synergistic effect obtained from such supplementation may improve rigidity, speech, walking disabilities, and depressive states commonly attributed to Parkinson’s. [9, 10]
The National Research Council has established recommended dietary allowances (RDAs) for phenylalanine, listed below:
|0 - 4 months||125 mg/per kilogram of bodyweight per day|
|5 months -2 years||69 mg/per kilogram of bodyweight per day|
|3 – 12 years||22 mg/per kilogram of bodyweight per day|
|13 +||14 mg/per kilogram of bodyweight per day|
Some adults may need to tailor intake to an allowance approaching 39 mg/per kilogram of bodyweight, to obtain physiological improvement. The median intake of phenylalanine ranges from 750 to 3,000 mg per day for adults.
In addition, 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.
A deficiency of phenylalanine is likely to occur if an individual’s protein consumption is inadequate. Signs and symptoms of a phenylalanine deficiency include; confusion, lack of energy, decreased memory, diminished appetite, edema, skin lesions, and decreased alertness. Extreme and prolonged deficiencies are often marked by liver damage and inhibited growth.
Additionally, an extremely rare inborn error exists, named Phenylketonuria (PKU). This condition occurs when an individual is born without the enzyme to properly metabolize phenylalanine. The metabolization of phenylalanine is critical in the conversion of toxic chemicals into nontoxic products, and for the transportation of important substances throughout the body.  The inability to carry out these important processes may lead to severe neurological damage, including mental retardation. Symptoms such as eczema, delays in physiological development, and hyperactivity are usually witnessed in these individuals within the first six months of age. Persons with PKU are forced to maintain a regimented eating plan, consisting of a phenylalanine-restricted, tyrosine-enhanced diet.
The amount of phenylalanine needed to produce toxicity in humans remains unknown. Transient headaches and nausea has, however, been reported when persons supplemented with amounts reaching nearly 1500 milligrams per day. More research is necessary.
Phenylalanine should be avoided by persons with PKU and tardive dyskinesia. Tardive dyskinesia (TD) is characterized by a condition of abnormal, repetitive, and uncontrollable movements, resulting from the long-term use of antipsychotic medications (e.g. schizophrenia). These individuals may suffer from an abnormality, which sharply inhibits the processing of phenylalanine.
1. 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.
2. Marik PE, Mohedin M. The contrasting effects of dopamine and norepinephrine on systemic and splanchnic oxygen utilization in hyperdynamic sepsis. JAMA 1994; 272(17):1354-1357.
3. Nutrition Data. “999 Foods; Highest in Phenylalanine.” (2004) http://www.pdrhealth.com/drug_info/nmdrugprofiles/herbaldrugs/101840.shtml
4. Budd K. Use of D-phenylalanine, an enkephalinase inhibitor, in the treatment of intractable pain. Adv Pain Res Ther 1983;5:305-8.
5. Walsh NE, Ramamurthy S, Schoenfeld L, Hoffman J. Analgesic effectiveness of D-phenylalanine in chronic pain patients. Arch Phys Med Rehabil. 1986;67(7):436-439.
6. Cormane RH, Siddiqui AH, Westerhoff W, Schutgens RB. Phenylalanine and UVA light for the treatment of vitiligo. Arch Dermatol Res. 1985;277(2):126-30.
7. Burkhart CG, Burkhart CN. Phenylalanine with UVA for the treatment of vitiligo needs more testing for the possible side effects. J Am Acad Dermatol. 1999;40(6 Pt 1):1015.
8. Sabelli HC, et al. Clinical studies on the phenylethylamine hypotheses of affective disorder: urine and blood phenylacetic acid and phenylalanine dietary supplements. J Clin Psychiatry 1986;47: 66-70.
9. Woodward WR, Olanow CW, Beckner RM, et al. The effect of L-dopa infusions with and without phenylalanine challenges parkinsonian patients: Plasma and ventricular CSF L-dopa levels and clinical response. Neurol. 1993;43:1704-170.
10. Heller B, Fischer E, Martin R. Therapeutic action of D-phenylalanine in Parkinson’s disease. Arzneimittelforschung 1976;26:577-9.
11. Recommended Dietary Allowances: National Academy of Sciences;10th ed., 1989
12. Glanze, W. (Ed.). (1996). The signet Mosby medical encyclopedia (revised edition). New York: Penguin Books Ltd.