People with phenylketonuria are advised that they should adhere to a low-phenylalanine diet for life. Phenylketonuria is caused by a metabolic defect that results in an abnormally high concentration of free phenylalanine in the blood, which produces excessive phenylpyruvic acid and inhibits protein synthesis and synapse formation, resulting in irreversible progressive damage to the brain and other organs. Patients with phenylketonuria should adhere to a low-phenylalanine diet for life, limiting their daily intake of phenylalanine to 250-500 mg, and periodically reviewing the value of phenylalanine in the blood and dynamically adjusting the dietary regimen according to the results. Patients with phenylketonuria need to monitor phenylalanine regularly under the guidance of a doctor to make adjustments to the treatment program.