The Truth About Aspartame

Packets of sweeteners sit on a table.
(Image credit: Sweetener packets photo via Shutterstock)

In 1965, James M. Schlatter, a chemist at G.D. Searle and Company, accidentally contaminated the tip of his index finger with an unassuming white powder. Later that day, a page in the book he was reading got stuck. He licked his fingertip to turn the page, and inadvertently gave birth to an entire industry, as well as a seemingly eternal controversy.

The substance on Schlatter's finger, 200 times sweeter than sugar, was aspartame, the artificial sweetener known today by the brand names NutraSweet, Equal and Spoonful. Almost 50 years after Schlatter discovered aspartame's incredible sweetness, disagreement still exists among scientists about whether it's safe for human consumption.

In essence, aspartame consists of two amino acids with an extra carbon atom stuck on one end. Aspartame breaks down completely into these three components in the small intestine, and they make their way separately into the blood.

One of aspartame's two amino acids, aspartic acid, is non-essential, which means the body can manufacture it from other raw materials. Aspartic acid is also a neurotransmitter, which has led to speculation that aspartame consumption affects normal brain processes, possibly causing headaches, migraines, or worse. Almost all dietary protein contains aspartic acid, however, and the aspartic acid found in artificially sweetened foods and drinks pales in terms of quantity to the amount gained through a normal diet.

However, phenylalanine, the other amino acid in aspartame, is another story – but only for the small subset of the population. Phenylalanine is an essential amino acid, which means the body can only acquire it through the diet. For sufferers of the disease phenylketonuria, ingesting this amino acid leads to a dangerous buildup of phenylalanine that can damage the brain.

Although the amino acids comprising the bulk of aspartame are harmless for most people, the scientific jury is still deliberating about that extra carbon atom tacked on the end of the molecule. When an aspartame molecule breaks apart in the small intestine, this carbon disengages from the amino acids and forms a single molecule of methanol.

Methanol, also known as wood alcohol, is found in antifreeze and rocket fuel, among many other applications. Methanol's effect on the body is similar in some ways to that of ethanol (the alcohol found in wine and beer), but unlike ethanol, the body deals with methanol by transforming it into waste products that include formaldehyde, a carcinogen that morticians use as embalming fluid.

If aspartame delivers methanol to your bloodstream, it would seem like a no-brainer to avoid the sweetener at all costs, but there's a confounding factor: methanol is also found in all sorts of harmless foods, especially fruits and vegetables, in quantities comparable to foods that contain aspartame. In fact, aspartame-flavored soda contains less than half the methanol found in the same volume of many fruit juices.

This is where the dialogue gets contentious. To some researchers, it's clear that methanol is harmless in the small quantities derived from aspartame-containing foods. However, a study conducted in 2005 by the European Ramazzini Foundation, which tracked the health of aspartame-fed rats for their entire natural lives, linked aspartame consumption with an increased lifetime cancer risk.

Some researchers, as well as the U.S. Food and Drug Administration, found fault with the study's methods, while other scientists rushed to defend it, saying that at the very least, aspartame requires continued examination. At the heart of the debate is the fact that in rats, as in humans, a large percentage of individuals will succumb to cancer in very old age. It's difficult for scientists to say whether cancer in a very old rat was caused by lifetime ingestion of a substance such as aspartame, or whether the cancer would have occurred naturally.

As the debate surrounding the long-term safety of aspartame persists, it's important to consider the sweetener not in terms of its absolute safety, but whether it's healthier than the alternative: sugar. Given rising levels of diabetes and obesity in the United States, it's possible that for some people, a zero-calorie sugar alternative that carries some risks may still be a healthier choice than sugar. And in the meantime, new artificial sweeteners such as sucralose are flooding the market, which may or may not carry their own health risks.

There is one sure-fire healthy alternative to both artificial sweeteners and sugar, of course. Put down that soda and toss back a glass of water, unsweetened coffee or tea, instead.

Pass it on: Aspartame is widely regarded as safe, but some doubts about its safety remain.

Food Facts explores the weird world of the chemicals and nutrients found in our food, and appears on MyHealthNewsDaily on Fridays. Follow MyHealthNewsDaily on Twitter @MyHealth_MHNDFind us on Facebook.

Read more Food Facts columns:

MyHealthNewsDaily Correspondent