The Food and Drug Administration (FDA) recommends people limit their intake of aspartame to 50 milligrams per kilogram of weight. Unless a person has Phenylketonuria, which is a genetic disorder, aspartame does not need to be avoided or restricted, since most studies have shown no correlation between aspartame and cancer.
The Food and Drug Administration's acceptable daily intake of aspartame is relatively high. A 165-pound person weighs about 75 kilograms. A person of this size can consume up to 3,750 milligrams of aspartame every day. One can of diet soda has about 192 milligrams of aspartame. A person would need to consume more than 19 cans of diet soda in a day to exceed the acceptable daily intake.
The body breaks down aspartame into phenylalanine, methanol and aspartic acid. Methanol is toxic in high doses, but many other foods produce more in the body. A liter of diet soda produces only 55 milligrams of methanol, while an equivalent amount of fruit juice produces 680 milligrams. Phenylalanine and aspartic acid are present in many foods with protein, and generally speaking they do not need to be avoided. For people with Phenylketonuria, phenylalanine needs to limited in their diet, and it is recommended that they avoid aspartame, among other foods.