Phenylalanine occurs naturally in many protein-rich foods, such as milk, eggs and meat. Phenylalanine is also sold as a dietary supplement. The artificial sweetener aspartame (Equal, NutraSweet), which is added to many medications, diet foods and diet sodas, contains phenylalanine.Click to see full answer. Then, what is phenylalanine and is it bad for you?Phenylalanine isn’t a health concern for most people. However, for people who have the genetic disorder phenylketonuria (PKU) or certain other health conditions phenylalanine can be a serious health concern. Phenylalanine can cause intellectual disabilities, brain damage, seizures and other problems in people with PKU.Beside above, what products contain phenylalanine? Phenylalanine is found in most protein-containing foods such as milk, eggs, cheese, nuts, soybeans, chicken, beef, pork, beans and fish. Secondly, what are the side effects of phenylalanine? Side effects may include: Heartburn. Fatigue. Nausea. Constipation. Dizziness. Headache. Anxiety and hypomania (a milder form of mania) Sedation. What is the purpose of phenylalanine?Phenylalanine is an amino acid found in many foods and used by your body to produce proteins and other important molecules. It has been studied for its effects on depression, pain and skin disorders.