Phenylalanine: Role of Amino Acid and Purpose in Diet

Medically reviewed by Aviv Joshua, MSMedically reviewed by Aviv Joshua, MS

Phenylalanine is an amino acid, a compound your body uses to make proteins. It's an essential amino acid, meaning you must get it from your diet because the human body can't produce it. When you consume phenylalanine, your body converts it into tyrosine, another amino acid, which is then used to produce important brain chemicals like dopamine, norepinephrine, and epinephrine.

Does Phenylalanine Occur Naturally in the Body?

Phenylalanine is one of 20 amino acids: nine essential and 11 nonessential. Your body can make nonessential amino acids if and when you don't consume enough of them in your diet. However, it cannot make essential amino acids, so you must include sources of these amino acids in your diet regularly.

Phenylalanine is an essential amino acid, meaning that phenylalanine does not naturally occur in your body. This amino acid has come from an external source, and once it's consumed, it's converted into tyrosine to help produce brain chemicals and proteins that your body needs.

Related: Understanding Amino Acids

Phenylalanine in Food and Drinks

Phenylalanine is found in many high-protein foods, such as animal proteins, and some plant-based sources like soy products and legumes (e.g., beans, peanuts, lentils).

Here's where you can find it:

• Beans and chickpeas

• Dairy products like milk, cheese, and yogurt

• Eggs

• Fish

• Foods made from the meat substitute Quorn made from fungi-based protein

• Gelatin

• Lentils

• Meat and poultry

• Nuts and seeds

• Oats, quinoa, rye, barley, and wheat germ
  

• Plant algae such as spirulina

• Soy foods like tempeh, tofu, and edamame

As an Added Ingredient

Phenylalanine may also be found in some foods as a byproduct of other ingredients or intentionally added to certain products.

It is most often found in "light" or "diet" beverages and foods that contain aspartame as an artificial sweetening agent. Aspartame is made of phenylalanine and another amino acid, called aspartic acid.

Otherwise, manufacturers may intentionally add it to certain protein powders, which often contain additional amino acids, including phenylalanine, to enhance protein content. The best way to know whether a protein powder or other protein-enhanced product (like a sports snack bar) contains phenylalanine is to read the ingredients label.

Supplements

Phenylalanine is readily available in many food sources, so it's not an amino acid most people need to supplement to meet their needs. However, there are some instances in which supplemental phenylalanine may make sense or be recommended by a healthcare provider, such as:

• Mental health support: The body needs phenylalanine to make dopamine, norepinephrine, and epinephrine, brain chemicals associated with mood regulation, alertness, and stress response. Some people may take phenylalanine supplements to help manage depression symptoms or to improve mood.

• Pain management: Researchers have studied phenylalanine for its potential to alleviate pain, particularly ongoing arthritis pain. Its pain management properties are thought to be due to how phenylalanine influences brain chemicals involved in pain signaling.

• Skin conditions: Research suggests that phenylalanine might help improve vitiligo, a condition that causes loss of skin pigment in patches. Phenylalanine is a precursor to melanin, a compound in the body that produces skin color.

• Protein synthesis: Some athletes and bodybuilders might take phenylalanine supplements as part of their amino acid intake to support muscle growth and repair, but research is limited on whether this is beneficial.

Before adding a phenylalanine supplement or any supplement to your health routine, speak with a healthcare provider or registered dietitian to see if it's safe and appropriate for you.

Safety and Phenylketonuria

Phenylalanine is an essential amino acid and is considered safe when consumed through a regular balanced diet for most healthy people—meaning you probably don't need to boost or track your phenylalanine intake.

However, people who have phenylketonuria (PKU) have to be cautious with how much they're getting. PKU is a rare inherited genetic disorder that affects how the body processes phenylalanine.

People with PKU have a deficient or nonfunctional phenylalanine hydroxylase enzyme, which converts it into compounds needed to make brain chemicals and regulate the amounts of amino acids in the body. Without this enzyme, phenylalanine builds up in the body and can become toxic.

If someone with PKU has too much phenylalanine in their body, it can be toxic to the brain and cause seizures, delays in brain development, behavioral problems, and mental health issues if not identified and appropriately treated.

Fortunately, PKU is usually diagnosed through routine newborn screening tests, which are done within a few days of birth to check for high levels of phenylalanine in the blood. As with other health conditions, earlier detection of PKU is better.

The primary treatment for PKU includes a lifelong diet that is strictly low in phenylalanine. A low-phenylalanine diet avoids high-protein foods like meat, dairy, nuts, and certain grains. Additionally, products containing aspartame must carry a warning for people with PKU.

People with PKU must monitor their phenylalanine levels with regular blood tests and adjust their diet accordingly. Sometimes, they may require tyrosine supplements since the amount of this amino acid may be low without phenylalanine.

How to Optimize Amino Acid Production

The best way to ensure you're getting all the amino acids you need is to eat a diet that incorporates adequate protein. While you may have heard that you should combine certain protein sources at the same time to ensure you get all the amino acids you need, this is a misconception, and there's no magic approach to this.

Your body is designed to combine the amino acids it needs (from your diet and the ones it makes) to make proteins, either by storing them or by breaking them down and removing the excess.

Some great sources of protein include:

• Certain whole grains, like quinoa
  

• Dairy products

• Eggs

• Legumes, including beans, peas, and lentils

• Meat and poultry

• Nuts and seeds

• Soy foods, like tofu and tempeh
  

Summary

Phenylalanine is an essential amino acid that most of us get more than enough of through protein sources in our everyday diets, whether we eat mostly animal-derived, plant-based, or a mix of both. If you have PKU, it's important to be aware of your phenylalanine intake and monitor your levels with the help of a healthcare provider.

Most people do not need to think twice about how much phenylalanine they're getting, as the body will use what it needs to make proteins and brain chemicals and eliminate the rest.

Read the original article on Verywell Health.