Aspartame is composed of methanol and two naturally occurring amino acids: aspartic acid and phenylalanine. Because asppartame breaks down into these amino acids in the body, it behaves like a protein, providing an energy value of 4 kcal/g. This energy value is the same as sugar, but since aspartame is used in only very small quantities, food and beverage manufacturers can advertise their products as "calorie-free." A review of aspartame's metabolism showed that the human body breaks down aspartame into three compounds: methanol, aspartic acid, and phenylalanine. Although methanol is toxic to the human body, research has established that the consumption of products containing aspartame will not lead to toxic levels of methanol. The same conclusion applies to aspartic acid. However, only a small amount of phenylalanine can cause severe brain damage in individuals with the genetic disease phenylketonuria. These individuals must avoid products with aspartame. To date, no substantial or conclusive evidence indicates that aspartame harms the rest of the population or slow metabolism.
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