Your body uses the amino acid phenylalanine to make another amino acid called tyrosine, which is a component of some of the brain chemicals, proteins and thyroid hormones that your body produces. For most people, not getting enough phenylalanine causes deficiency symptoms. However, for some people, consuming phenylalanine is dangerous.
Phenylketonuria
Some people are born with a rare condition that makes it impossible for them to break down and use phenylalanine. This means that phenylalanine can build up in the body to dangerous levels if the condition, called phenylketonuria, or PKU, is not treated in a timely manner. For a baby to be born with PKU, both parents must have the defective gene that causes this condition, MedlinePlus says.
Brain Damage
Most people have no trouble using the phenylalanine they consume, so there's no risk of getting brain damage because of high phenylalanine. However, if a baby has PKU and it isn't treated soon after birth with a special diet, she may develop irreversible brain damage, causing mental retardation, MedlinePlus says. The longer a child is untreated, the more likely she will develop brain damage from high phenylalanine levels.
Prevention
To prevent this type of brain damage, babies in the United States are tested for PKU while in the hospital after being born. If a baby has PKU, he can be immediately put on a special diet that is low in phenylalanine. For best results, he should stay on this diet for the rest of his life.
Considerations
It can be hard to follow a low-phenylalanine diet. This amino acid is present in many common foods, including milk, eggs, many foods containing protein and aspartame. People with PKU, including infants, must consume special beverages that contain protein but little or no phenylalanine, and they may need to take supplements as well to meet their nutrient needs, according to the University of Maryland Medical Center.
If you don't have PKU, you don't have to worry about high phenylalanine levels unless you take phenylalanine supplements, in which case your dose should not exceed 5,000mg per day or you may develop nerve damage.
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