Phenylalanine is an amino acid found in many foods.
It exists in two forms — L-phenylalanine and D-phenylalanine. They’re nearly identical but have slightly different molecular structures.
Because your body cannot produce enough L-phenylalanine alone, it’s an essential amino acid, meaning you must get it from your diet. Good sources include high-protein foods like eggs, dairy, meat, and soy products.
Your body uses L-phenylalanine to make proteins and other important molecules. It has also been studied as a treatment for several medical conditions, including skin disorders and depression.
However, it can be dangerous for people with the genetic disorder phenylketonuria (PKU), which impairs the body’s ability to metabolize phenylalanine.
This article explains all you need to know about phenylalanine, including its benefits, side effects, and food sources.
Phenylalanine is important for many bodily functions
Your body needs phenylalanine and other amino acids to make proteins found in your brain, blood, muscles, internal organs, and virtually everywhere else in your body.
Phenylalanine is also crucial for the production of other molecules, including:
- Tyrosine. This amino acid is produced directly from phenylalanine. Your body uses it to make new proteins or converts them into other molecules like epinephrine.
- Epinephrine and norepinephrine. When you experience stressful situations, these molecules are vital to your body’s fight or flight response.
- Dopamine. This neurotransmitter is an important part of your brain’s reward center and is involved in motor control, memory, and learning.
The dysfunction of these molecules can cause negative health effects, such as depression.
Since your body uses phenylalanine to make these molecules, it has been studied for its link to major depressive disorders.
Summary: Your body can convert phenylalanine into the amino acid tyrosine, which is then used to produce other important molecules. These molecules are involved in several health aspects, including mood, brain function, and stress responses.
Benefits of phenylalanine
Several studies have examined how phenylalanine might benefit the treatment of certain medical conditions.
Some research indicates that taking phenylalanine supplements alongside ultraviolet (UV) light treatment may improve skin pigmentation in individuals with vitiligo, a skin condition that causes loss of skin pigment.
Phenylalanine can also produce dopamine, which is key to mental health and depression.
In a small, older study from 1977 including 12 people with depression, two-thirds of the participants experienced improved symptoms after taking a mixture of the D- and L-forms of the amino acid.
Newer studies have found low phenylalanine levels could be linked to major depressive disorder.
On the other hand, other older research shows no clear benefits. Ultimately, because there’s limited recent research available on the effects of phenylalanine on depression, more high-quality studies are needed.
In addition to vitiligo and depression, phenylalanine has been studied for potential effects on:
- Pain. Some older studies have found that D-phenylalanine might relieve pain, but research has yielded mixed results overall.
- Alcohol withdrawal. According to a 2011 study, using a supplement containing D-phenylalanine and other amino acids could help alleviate symptoms of alcohol withdrawal.
- Parkinson’s disease. An older study suggests that phenylalanine may support Parkinson’s disease treatment, but more research is needed. Although inconclusive, tyrosine has also been studied for its effects on brain function and Parkinson’s.
- ADHD. Research does not indicate that this amino acid has any benefits for treating attention deficit hyperactivity disorder (ADHD).
Summary: Phenylalanine may improve the skin disorder vitiligo when combined with UV treatment. At this time, studies do not support the use of this amino acid to treat other conditions.
Dangers and side effects of phenylalanine
Phenylalanine is found in many protein-containing foods and is generally considered safe by the Food and Drug Administration (FDA).
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The amount found naturally in foods likely doesn’t pose a risk for healthy individuals. Moreover, few or no side effects are generally observed at supplement doses up to 12 grams daily.
Nevertheless, it’s best to use phenylalanine only as directed and check with your doctor before adding any supplements to your routine.
People taking medications for schizophrenia should avoid using phenylalanine, as it could worsen symptoms of tardive dyskinesia, a condition characterized by involuntary, repetitive movements.
Those who are pregnant or breastfeeding should also avoid taking phenylalanine supplements, as there’s limited research on their safety and potential long-term effects.
Furthermore, those with phenylketonuria (PKU) should carefully monitor their amino acid intake. This disorder impairs the body’s ability to metabolize phenylalanine, leading to high blood levels.
Dangerously high blood concentrations of phenylalanine can cause severe brain damage, delayed growth, intellectual disability, and problems transporting other amino acids to the brain.
PKU is also associated with several other disorders, including epilepsy, overactive reflexes, and neurological issues like tics or tremors. Due to the seriousness of this disorder, newborns are generally screened for it soon after birth.
Individuals with PKU are placed on a special low-protein diet to limit their intake of phenylalanine, which is generally maintained for life.
Summary: For healthy adults, phenylalanine is considered safe in the quantities found naturally in foods. However, individuals with phenylketonuria (PKU) cannot metabolize it and must minimize their intake to prevent adverse health effects.
Foods high in phenylalanine
Many high-protein plant and animal foods contain phenylalanine, including meat, fish, poultry, and legumes.
It’s also found in aspartame, an artificial sweetener often added to diet soda and many sugar-free foods.
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Here are some of the top food sources of phenylalanine:
- Meat: beef, pork, lamb, venison
- Poultry: chicken, turkey, duck, goose
- Seafood: salmon, trout, tuna, mackerel, shrimp, lobster
- Eggs: whole eggs, egg whites
- Dairy: milk, cheese, yogurt
- Nuts: almonds, pistachios, macadamia nuts, cashews, walnuts
- Seeds: pumpkin seeds, squash seeds, hemp seeds, sunflower seeds
- Nut butter: peanut butter, almond butter, cashew butter
- Legumes: lentils, chickpeas, black beans, kidney beans
- Whole grains: quinoa, oats, rye, barley, wheat
- Soy products: soybeans, tofu, tempeh, edamame, protein supplements
- Diet products: diet soda and sugar-free ice cream, gum, candies, and flavored yogurts made with aspartame
Generally, you don’t need to select foods based on their phenylalanine content. Instead, eating various protein-rich foods throughout the day will provide you with all the phenylalanine you need and other essential amino acids and nutrients.
Summary: Many foods contain phenylalanine, including soy products, eggs, seafood, and meats. Eating various protein-rich foods throughout the day will provide the amino acids your body needs, including phenylalanine.
Phenylalanine is an essential amino acid found in both plant and animal foods.
It may benefit the skin disorder vitiligo, but research on its effects on depression, pain, and other conditions is limited.
While it’s generally considered safe for healthy individuals, it’s important that those with phenylketonuria (PKU) keep their intake low to avoid potentially dangerous side effects.
Talk with your doctor if you notice any negative side effects after taking a phenylalanine supplement or eating high-protein foods.
They can test your amino acid blood levels and help determine your best treatment.