Phenylalanine is an amino acid found in most proteins and in the artificial sweetener aspartame. Clinical research has shown that aspartame is not an allergen, notes the U.S. Department of Health and Human Services. However, some people may not be able to effectively metabolize phenylalanine due to a genetic disease called phenylketonuria, or PKU. High phenylalanine levels in the body can cause brain damage.
Symptoms
Babies born in the United States and in many other countries receive screening for PKU soon after birth, according to MayoClinic.com. Babies with untreated PKU will typically develop symptoms within several months. The body's failure to transform phenylalanine into the pigment melanin may lead to fair skin and blue eyes, and high phenylalanine in the body may lead to a musty odor in a child's breath, skin or urine. More severe symptoms may include mental retardation, behavioral problems, seizures, tremors or jerking movements, hyperactivity, stunted growth, skin rashes and small head size, or microcephaly.
Low-Phenylalanine Diet
A diet with strictly limited phenylalanine intake can prevent the development of severe symptoms, according to MayoClinic.com. People with PKU, often called phenylketonurics, should avoid all high-protein foods, including milk, eggs, cheese, nuts, beans, soybeans, chicken, steak, beef, fish, chocolate and peas, as well as medications, artificial sweeteners and diet sodas made with aspartame. Adults and children with PKU should limit their intake of several other types of foods, including pasta, rice, bread, cookies and some fruits and vegetables. Babies with phenylketonuria must consume a specialized phenylalanine-free formula. Doctors used to allow PKU patients to go off the low-phenylalanine diet in their adolescent years. Doctors now recommend that PKU patients remain on the diet for life, however.
PKU and Pregnancy
Pregnant women with a history of PKU must carefully follow a low-phenylalanine diet. High-phenylalanine blood levels in a pregnant woman may harm the developing fetus, causing the baby to be born with low birth weight, heart defects, microcephaly or mental retardation.
Tests
Your doctor can determine a safe amount of phenylalanine for your diet based on diet records, growth charts and levels of phenylalanine in your blood, according to MayoClinic.com. Phenylketonurics need frequent blood tests during childhood and pregnancy to monitor changes in phenylalanine levels.
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