Phenylalanine is an essential amino acid. Amino acids are building blocks for protein in the body. Essential amino acids cannot be manufactured by the body, so you must obtain them from food. Many foods contain phenylalanine, including the sweetening ingredient aspartame that is used to make various diet and sugar-free drinks and snacks. People with the medical condition phenylketonuria must avoid phenylalanine.
Phenylalanine Functions
There are three forms of phenylalanine. L-phenylalanine is the natural form in food and proteins. D-phenylalanine and DL-phenylalanine are made in a laboratory. Your body changes phenylalanine into tyrosine, another amino acid. Tyrosine is used to make proteins, especially brain chemicals like L-dopa, epinephrine and norepinephrine, and thyroid hormones. Phenylalanine deficiency can cause confusion, decreased alertness, memory problems, depression, and lack of energy and appetite.
Phenylalanine Requirements
The recommended daily allowance for phenylalanine is based on age and body weight. Infants up to 4 months need 57 mg per pound; children 5 months to 2 years need 31 mg per pound; children 3 to 12 years need 10 mg per pound; teenagers and adults need 6 mg per pound.
Phenylketonuria
Phenylketonuria (PKU) is a rare genetic disorder in which the body does not make an enzyme needed to metabolize phenylalanine. If the phenylalanine level gets too high, it can cause severe brain damage. Babies born in U.S. hospitals are screened for PKU. People with PKU follow a low-protein diet to avoid phenylalanine, and take tyrosine supplements to support brain growth and development.
Phenylalanine in Food
All foods derived from animal protein contain phenylalanine, including meat, fish, poultry, milk, yogurt, cheese and eggs. It is also present in some vegetable proteins, including soy products, and some nuts and seeds. The artificial sweetener aspartame also contains phenylalanine.
Aspartame
The artificial sweetener aspartame has been available in the U.S. since 1981. It is made from the amino acids phenylalanine and aspartic acid. The FDA has set an acceptable daily intake level, and consumption studies have shown that actual intake is significantly lower than the acceptable intake level. Aspartame is available as a tabletop sweetener and is found in beverages, chewing gum, desserts and cereals. Aspartame has been thoroughly tested and found to be safe, yet those with PKU are still advised to avoid foods that contain the sweetener.
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