Wednesday, Jun. 16, 2010

Ask the Doctor: What is phenylalanine?

Question:

I have noticed that certain food packages, such as soda cans, have the phrase "PHENYLKETOURICS:CONTAINS PHENYLALANINE". What is the meaning of this?

R.F., Chowchilla, CA

Answer:

Phenylketonurics are individuals that have the disease called phenylketonuria. Phenylketonuria, known by the abbreviation PKU, is caused by a genetic birth defect. A defective gene causes the liver not to produce an enzyme needed to metabolize (break down) a specific protein called phenylalanine. Since phenylalanine can not be metabolized, it is transformed into phenylketone which is found in the urine. Therefore, patients with high levels of phenylketone in their urine are called Phenylketonurics.

Amino acids are the building blocks for protein. Phenylalanine is one of these amino acids. However, if the body is unable to metabolize this amino acid, it will accumulate to high levels and cause significant health problems. This can happen when a person with PKU eats foods high in protein, such as cheese, meats, milk and nuts.

All infants born in the USA are routinely screened for phenylketonuria at birth; it is relatively rare. However, if detected immediately, major health problems can be prevented. The disease interferes with brain development, and may cause mental retardation , seizures, behavioral and other problems. Newborn infants with phenylketonuria usually do not have any symptoms. Symptoms can appear within a few months after birth. However, when recognized early, with appropriate treatment, the disease manifestations can be prevented.

The main treatment for phenylketonuria includes a strict diet that limits phenylalanine, which is present in high protein foods. Examples of such foods includes milk, cheese, eggs, nuts, beef, chicken, fish, chocolate, etc. Phenylketonurics should also avoid any foods that may contain aspartame (Equal, etc.) . Aspartame is an artificial sweetener that has high levels of phenylalanine; many diet sodas contain aspartame.