How dangerous is aspartame?

The metabolism of aspartame and the proposed toxicities from these metabolites have concerned many people and have been the emphasis of various postmarketing surveillance studies.

Aspartame is metabolized by digestive esterases and peptides to three common dietary components: amino acids, aspartic acid and phenylalanine. (Minute amounts of methanol can also be detected.) Eating foods such as meat, milk, fruits and vegetables will also produce these same components, but in greater amounts than aspartame. For example, a glass of milk has six times more phenylalanine and 13 times more aspartic acid, and a glass of tomato juice provides six times more methanol than a beverage the same size sweetened with 100% aspartame. Interestingly enough, it is impossible for humans to digest enough aspartame to raise the levels of these metabolic components to a dangerous level. 
Robert  Davis, PhD
Health Education
On the Internet you can find plenty of scary warnings about the artificial sweetener aspartame causing everything from memory loss and depression to brain tumors and birth defects. But decades of research have turned up little hard evidence for such assertions.

Though Italian researchers have found elevated rates of lymphoma, leukemia, and other cancers in rodents ingesting aspartame, most other animal studies have shown no connection between aspartame and cancer. More important, in a cohort study involving nearly 500,000 people, there was no increased risk of blood or brain cancers among aspartame users.

Likewise, most studies looking at neurological and behavioral issues haven't found adverse effects from aspartame. When a panel of scientists reviewed more than 500 studies, they uncovered no major safety problems. The review was funded by a Japanese manufacturer of aspartame, but the experts were unaware of who the funder was, and the company had no role in selecting the experts.

The panel's conclusions echo those of both the US Food and Drug Administration and the European Commission's Scientific Committee on Food, which say that a daily intake of up to 40 or 50 milligrams of aspartame per kilogram of body weight is safe for most people. Translated into plain English, this means a 150-pound adult can safely consume up to about 19 cans of diet soda a day. (Not that anyone says drinking this much is advisable.)

Still, aspartame may adversely affect certain people. One of the most common complaints is headaches, an effect detected by some (but not all) research. Also, people with a rare inherited condition called phenylketonuria (PKU) can't metabolize phenylalanine, an amino acid in aspartame. To avoid an unsafe buildup, they need to steer clear of the sweetener. (Hence that cryptic warning "Phenylketonurics: Contains Phenylalanine" on the labels of foods and beverages that contain aspartame.)

Despite the claims of some aspartame opponents, there's no solid proof that phenylalanine from normal amounts of aspartame poses a danger to the rest of us. The same goes for methanol, which is also produced when our bodies break down aspartame.

Those who are convinced aspartame is poison or an evil plot may denounce me as an ignoramus or a pawn of industry for not agreeing with them. But at least they won't be able to blame my "confusion" on aspartame-related brain problems. Personally, I can't stand the taste.
Aspartame, the artificial sweetener found in NutraSweet, has been extensively studied since it was approved by the FDA in 1974. Despite numerous articles and claims that aspartame may cause cancer and other deleterious effects on the human body, a 2007 review of all the evidence concluded “The weight of existing evidence is that aspartame is safe at current levels of consumption as a nonnutritive sweetener.” This has been supported by numerous medical bodies including the American Academy of Family Physicians.

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Important: This content reflects information from various individuals and organizations and may offer alternative or opposing points of view. It should not be used for medical advice, diagnosis or treatment. As always, you should consult with your healthcare provider about your specific health needs.