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Phenylalanine

Phenylalanine is an essential amino acid that is found in almost all foods. It was isolated from plant sources in 1879 and chemically synthesized in 1882. Phenylalanine and, depending on it, tyrosine contribute to the synthesis of important endogenous proteins. These include, for example, insulin, papain and melanin as well as the thyroid hormone thyroxine. Phenylalanine can be converted into messenger substances required by the brain (neurotransmitters dopamine, serotonin and tyramine) and thus has stimulating effects. It can improve memory performance and curb appetite. Phenylalanine is also required for the removal of harmful substances by the kidneys and bladder. Phenylalanine is converted to tyrosine in the liver, which can only be produced from this amino acid.

Tyrosine is then converted into other substances, hormones and neurotransmitters. Tyrosine is, for example, a precursor of the skin pigment melanin, and it contributes to the production of the thyroid hormone thyroxine. This process is disrupted under severe stress, for example due to infections, trauma or chronic illnesses. Tyrosine then becomes an essential amino acid. Unlike other amino acids, phenylalanine not only has special functions in the body in its natural L-form, but also as a D-form. It is believed that D-phenylalanine can block enzymes in the central nervous system that break down the body's own "painkillers". If they are inhibited, certain substances (enkephalins) can relieve pain more effectively. D-phenylalanine also has antidepressant properties, but it is mainly used to relieve chronic pain. Synthetically produced DL-phenylalanine combines both forms and their abilities.

The main sources of phenylalanine

Phenylalanine is found in many foods. It is abundant in vegetables, nuts, seeds, wheat germ, dairy products, meat and fish. Some phenylalanine-rich foods contain the following per 100 grams

  • Soybeans 1970 mg
  • Emmental cheese 1800 mg
  • Peanuts 1540 mg
  • Wheat germ 1200 mg
  • Almonds 1400 mg
  • Tuna 1050 mg
  • Beef, fillet 930 mg
  • Trout, blue 920 mg
  • Cottage cheese 635 mg
  • 1 medium egg 400 mg

Typical groups for an increased phenylalanine requirement

  • for acute, chronic stress (infections, trauma, sport, etc.)
  • D- or DL-phenylalanine for chronic pain
  • possibly for depression
  • Tyrosine possibly for alcohol withdrawal
  • Tyrosine possibly for phenylketonuria (if tyrosine levels are low)
  • in the case of a general lack of amino acids due to certain diseases
  • in Parkinson's disease

Phenylalanine contributes to many functions in the body through its involvement in hormone metabolism and the formation of important neurotransmitters. D-phenylalanine (and DL-phenylalanine) has a soothing effect, especially in chronic pain. DL-phenylalanine can also support the pain-relieving effects of acupuncture. There are indications that DL-phenylalanine can help with withdrawal from alcohol or other drugs. In Parkinson's disease, phenylalanine can help to increase the neurotransmitter dopamine and alleviate the symptoms of the disease.

When phenylalanine is lacking in the body

Phenylalanine deficiency is rare. It disrupts the biosynthesis of proteins. One of the consequences, for example, is that the formation of myelin sheaths (insulating protection of nerve fibers) in the brain is disrupted. This can lead to neurological damage. People who have phenylketonuria must ensure that they consume sufficient amounts of phenylalanine in their diet while limiting their intake. Like phenylalanine, tyrosine, which is dependent on phenylalanine, is rarely lacking. The need for tyrosine increases during acute, chronic stress. Stress lowers noradrenaline levels, which are controlled by the adrenal glands.

When phenylalanine is present in excess

Phenylketonuria is an inherited, congenital and globally widespread metabolic disorder. In Germany, around 1 in 7,000 newborns is affected. All infants are tested in order to detect this disorder at an early stage and prevent its consequences. In phenylketonuria, the body lacks a liver enzyme (phenylalanine hydroxalase) that converts phenylalanine into the amino acid tyrosine. As phenylalanine cannot be broken down in the body, very high levels of the amino acid accumulate in the blood (>400 times higher than normal), which ultimately leads to poisoning. The skin, hair and brain are particularly affected. The disease leads to slower mental development and can cause brain damage, seizures and skin disorders. If phenylketonuria is detected during newborn screening, it can be treated with a lifelong and consistent diet and normal mental development can be achieved. As our many protein-containing foods provide more phenylalanine than the body needs, special products are used from which phenylalanine has been removed.

Is it possible to overdose on phenylalanine or are there side effects?

Phenylalanine is dosed for therapeutic purposes and should therefore be taken under therapeutic supervision. Side effects are possible in rare cases with phenylalanine. These include, for example, headaches, anxiety and high blood pressure. Phenylalanine should not be taken in the case of certain illnesses, such as severe liver disease, when taking certain antidepressants (MAO inhibitors) and in schizophrenia, when dopamine levels are elevated.