Aspartame is a low-calorie sweetener composed of two amino acids, aspartic acid and phenylalanine, and methanol.  After consuming foods or drinks containing aspartame, the body breaks down the sweetener into various components.  So, aspartame itself never enters the blood stream.  The amino acids and methanol are processed the same as if were ingested naturally.  The amino acids are used for energy and muscle mass, while methanol is converted and used as carbon dioxide and water.