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Phenylalanine is an essential amino acid. This means it must be obtained through the diet in adequate quantities to meet the body's needs.

Phenylalanine serves in the body as a precursor to the catecholamine family of hormones. The catecholamines include adrenaline and noradrenaline, which are activating substances in the central and peripheral nervous systems as well as being produced by the adrenal medulla (adrenal gland).

Therapeutic doses of phenylalanine may have useful roles in management of blood pressure disorders and control of certain forms of depression. Both low blood pressure and elevated blood pressure have been normalized by administration of therapeutic doses of phenylalanine and tyrosine. Therapeutic doses used in humans range between 300 and 1,500mg per day. It is best to administer these amino acids along with a carbohydrate source in the diet to facilitate absorption into the nervous system. Contraindications of phenylalanine supplementation are in those who display a hyper-functioning nervous state (anxiety) that may be aggravated by adrenaline. Supplementation with phenylalanine in these people can actually amplify the problem. Phenylalanine is known to be the antagonist of tryptophan. Whereas tryptophan has been used to induce sleep, phenylalanine has been used to increase states of arousal. Phenylalanine supplementation should be discontinued if headaches result.

Recommended Dietary Allowances

The RDA for phenylalanine has been established as 112mg per day for women and 110mg per day for men.

Food Sources

Foods high in phenylalanine include:

Cottage cheese - dry2,300 mg/cup
Cottage cheese - creamed1,647 mg/cup
Fish and other seafoods3,000-4,500 mg/lb.
Meats1,000-4,500 mg/lb.
Poultry2,000-4,500 mg/lb.
Peanuts, roasted with skin3,500 mg/cup
Sesame seeds3,000 mg/cup
Dry, whole lentils2,500 mg/cup

Method of Action

Phenylalanine can be converted to tyrosine by way of an enzyme called phenylalanine hydroxylase. Phenylalanine has been shown to be genetically impaired in some individuals, resulting in a disorder called phenylketonuria.

In these cases, a phenylalanine-restricted diet must be administered in infancy or mental retardation will result. The sweetener aspartame contains phenylalanine as part of its chemical makeup. Feeding this sweetener at high levels to individuals with the tendency toward phenylketonuria can aggravate their problem.


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Jones, M.R., Kopple, J.D., & Swendseid, M.E. Phenylalanine Metabolism in Uremic and Normal Man. Kidney Int., 14:169-79, 1978.

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