Aspartame has been used in the United States since the early 1980s. It is now found in thousands of different food products. Aspartame is commonly used as a tabletop sweetener, as a sweetener in prepared foods and beverages, and in recipes that do not require too much heating (since heat breaks down aspartame). It can also be found as a flavoring in some medicines.
In the body, aspartame is broken down into phenylalanine, aspartic acid, and methanol. Methanol can be toxic in high amounts, but the amounts that result from the breakdown of aspartame is lower than with many “natural” foods. For example, drinking a liter of diet soda would lead to consumption of 55 milligrams (mg) of methanol, as compared to as much as 680 mg of methanol from a liter of fruit juice.
Phenylalanine and aspartic acid are amino acids and are naturally present in many foods that contain protein. They do not cause health problems in most people. However people with the disease phenylketonuria (discussed in more detail later on) need to restrict their intake of phenylalanine, and so are usually counseled to avoid aspartame.