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amino acid
phenylalanine
Nutrition

definition

D,L-Phenylalanine (DLPA)

» an essential amino acid

» metabolism:
• Phenylalanine is the precursor for tyrosine. Many of the conditions that tyrosine is used for may also respond to phenylalanine. DLPA is considered to be one of the essential amino acids. It is also one of the aromatic amino acids.
• Phenylalanine is metabolized primarily by the liver through the action of phenylalanine hydroxylase. This enzyme directly metabolizes DLPA into tyrosine except in PKU and also in the synthesis of a metabolite tyramine. It is considerably better absorbed than tyrosine.

NOTE: DLPA follows a slightly different metabolic pathway than tyrosine as it forms an important brain neurotransmitter, phenylethylamine (PEA). PEA is a compound that has amphetamine like actions in the brain. Chocolate contains significant amounts of it.

• DLPA is normally found free in the blood stream. But in the brain it is found to be part of other important brain proteins, peptides and neurotransmitters.
• One defect in DLPA metabolism is Phenylketonuria (PKU) which was first identified in 1934. It was then discovered that 1% of the institutionalized retarded population was high in phenylpyruvic acid. From 1965-70 states adopted newborn screening programs to detect phenylketonuria. Occurrence is 1 in 5,000 births with the heterozygous condition occurring in as high as 1% of the population. 97% of cases show a deficiency of phenylalanine hydroxylase, the enzyme that converts DLPA into tyrosine. Children who are not treated with a restricted diet may become severely retarded. Treatment should begin as early as possible. Certain forms of PKU may be resistant to restriction of the diet. These cases have responded favorably to large amounts of folate supplementation.
(Marz, p. 90, 1997)

» function:
• Constituent of brain neuropeptides, somatostatin, vasopressin, melanotropin, ACTH, vasoactive intestinal peptide, angiotensin II and cholecystokinin, and so is chiefly involved with brain chemistry.
• Precursor to tyrosine.
• Converted to phenylethylamine, a possible excitatory neurotransmitter.
• Enkephalinase inhibitor which increase amounts of prostaglandins and enkephalins.

» Chinese:
• Relieves the Surface; clears Heat; dissolves Toxins; raises Clear Yang; activates the Qi; stops pain; contraindicated in Yin Xu (Deficiency) and Fire Xu (Deficiency) Patterns.

» requirements:
RDA: 1 g per day.
• Average intake in the U.S.: 4-5 g per day.
• Therapeutic range: 1.0-8 g per day.

NOTE: Children with PKU should be restricted to 60 mg phenylalanine/kg/day.

» food sources:
meat, cheese, wheat germ, aspartame (Nutrasweet®)

Best Sources of Phenylalanine
Food Amount Mg
Cheese, cottage 2% fat 1 cup 1700
Chicken 3 oz 1100
Cheese, cheddar 3 oz 1116
Turkey 3 oz 950
Tuna 3 oz 776
Cod, Atlantic cooked 3 oz 776
Salmon, Chinook 3 oz 666
Granola 1 cup 650
Wild game 3 oz 600
Pork 3oz 540
Oatmeal flakes 1 cup 500
Soybeans 1/2 c cooked 480
Milk, whole 1 cup 400
Chocolate 1 cup 400
Yogurt 1 cup 400
Meat, luncheon 3 oz 390
Wheat germ, toasted 1/4 cup 350
Egg 1 med 350
Bread, whole wheat 2 slices 285
Walnuts 10 whole 265
Cashews 10 nuts 250
Duck 3 oz 240
Sausage 3 oz 185
Avocado 1/2 med 75
(USDA: Composition of Foods. USDA Handbook #8 Washington DC, ARS, USDA, 1976-1986)

» deficiency:
• A deficiency of DLPA may lead to depression and diminished growth.

» therapeutics:
Depression: 1-6 g per day. Certain types of depression may respond favorably to DLPA. There have been a significant number of controlled trials which showed improvement comparable to many of the common antidepressants that are used. It may be more effective than tyrosine in the treatment of depression because of its ability to make PEA which is often deficient in depressed people. (Marz, p. 91, 1997)
Pain, chronic: DLPA may block certain enzymes such as enkephalinase, which normally breaks down enkephalines, and endorphins which have morphine like activity in the body. The endorphins and enkephalines have mild mood enhancing effects, but stronger analgesic effects. Such conditions as OA, PA, low back pain, menstrual cramps, and migraine headaches may respond to DLPA. (Marz, p. 91, 1997)
Parkinsons disease: 750 mg three times per day. DLPA may help with symptoms of rigidity and depression but not the tremors.

» dosage:
• 100 - 500 mg per day.

» toxicity:
• DLPA may cause symptoms of anxiety, jitteriness and hyperactivity in children.
• Sufferers of phenylketonuria must avoid DLPA.
• Children with attention deficit disorder or hyperactivity may need to avoid foods containing aspartamine (Nutrasweet).
• It may also cause problems with migraine headaches and hypertension due to tyramine sensitivity because phenylalanine may lead to an increase in tyramine levels.

» contraindications:
Phenylketonuria

» interactions:
• Tyramine containing foods may potentiate the effects of DLPA. People taking significant amounts of DLPA and eating tyramine containing foods may possibly have an increase in blood pressure. Caution must also be used with patients who are taking monoamine oxidase inhibitor type antidepressant medications since phenylalanine can precipitate a hypertensive crisis and there have been reports of cerebral hemorrhaging.


footnotes

Braverman and Pfeiffer pp. 29-43.

Marz, Russell. Medical Nutrition From Marz. Second Edition. Portland, OR. 1997

USDA: Composition of Foods. USDA Handbook #8 Washington DC, ARS, USDA, 1976-1986