You might have seen warnings on some gum and other foods that note the presence of phenylalanine, which is an amino acid. If you're wondering whether it's safe to consume phenylalanine during pregnancy -- given the warning labels -- the answer is that it certainly is, unless you have a disease called PKU.
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Phenylalanine is an amino acid and one of the building blocks of protein. Many of the proteins you take in when you eat food -- especially soy, meat, eggs and dairy -- contain phenylalanine, which you can burn for energy, use to make proteins in your body and use to make a variety of other molecules, including the neurotransmitters dopamine and norepinephrine, explains Dr. Lauralee Sherwood in her book "Human Physiology."
Phenylalanine isn't dangerous for the average person, but if you have a disease called phenylketonuria, also called PKU, you can't metabolize phenylalanine and it can build up in your body. You then convert it into a variety of compounds collectively called phenylketones, explains PubMed Health. These can cause physical and mental damage, particularly in babies and children. Those with PKU have to consume a low-phenylalanine diet, especially in childhood.
Gums, candies and other foods sweetened with aspartame contain phenylalanine, even if they don't contain any protein. This is because the aspartame molecule contains two amino acids: aspartic acid and phenylalanine. The amino acids, bonded together as they are and with the additional modification of a methyl ester group, bind to the sweetness receptor in your mouth, leading to the sweet flavor of aspartame. If you have PKU, you can't consume aspartame.
As long as you don't have PKU, aspartame and the phenylalanine contained therein won't hurt you. In fact, a healthy, balanced diet for someone who doesn't have PKU contains large amounts of phenylalanine, and any aspartame you consume adds only a small fraction of the total amount. If you do have PKU, however, it's important to avoid gum with aspartame, since the phenylalanine that builds up in your body can damage your fetus.