Aspartame is composed of three different ingredients: the amino acid phenylalanine, aspartic acid and methanol. Methanol is considered by many to be the most problematic ingredient, since its other name is wood alcohol. It can be toxic at certain levels. Aspartame is rapidly absorbed, and its constituent ingredients go through specific breakdown pathways. Aspartic acid is converted first to another amino acid, alanine, and to oxaloacetate, a component of the citric acid cycle, which results in the production of cellular energy. Phenylalanine is enzymatically converted into the amino acid tyrosine, which is itself the precursor of a number of vital body substances, such as melanin, the primary skin-coloring pigment, and the brain chemicals epinephrine, norepinephrine and dopamine, collectively known as catecholamines. Along with the trace mineral iodine, tyrosine is a component of thyroid hormones.
Methanol, on the other hand, converts into formaldehyde, then formic acid. That's where the primary controversy about aspartame arises, since formaldehyde is toxic and a potential carcinogen, or cancer-causing substance.
Various reports over the years, many of which circulate over the Internet, implicate aspartame in several health problems-hair loss, depression, dizziness, dementia, behavioral disturbances, adverse mood changes, impaired vision and headaches. Aspartame is also allegedly involved in the onset of several types of cancer, notably brain tumors.
Government commissions in the United States, Europe and Japan have examined the many claims of harmful health effects made about aspartame and dismissed them. That hasn't silenced the critics, however, who dismiss the government findings as another example of government and industry collusion. The implication is that human health and well-being are sacrificed in the name of corporate profit.
The newest report on the safety of aspartame initially appears to confirm the dangers of ingesting this sweetener.1 Published by a group of Italian researchers, it showed that when aspartame was given to rats in doses equal to less than half of the currently acceptable daily intake, the rats showed increased incidence of malignant tumors, lymphomas and leukemia. The authors began studying the rats at eight weeks old and continued to follow them until they died, giving them various doses of aspartame as part of their feed. Unlike earlier studies about aspartame safety, this one followed the rats for a longer time and examined them after death for microscopic changes that may have occurred.
Both male and female rats experienced increased incidence of various types of cancer. The authors speculate that the immediate cause was likely the methanol content of aspartame, since methanol degrades into known carcinogenic compounds.
Does that mean that aspartame is dangerous after all? No concrete evidence shows that it causes any type of cancer in humans. Rats are far more prone to cancer than humans, and doses of chemicals that cause cancer in rats have no effect in humans whatsoever.
Another problem is the suggestion that methanol is the probable smoking gun. Aspartame contains 10 percent methanol by weight, and a liter of a beverage containing aspartame would have 50 milligrams of methanol, far less than is found in an average serving of most fruit juices. If methanol is the problem, fruit juice should also be carcinogenic, which it's not. A study in which human subjects got 75 milligrams of aspartame per kilogram of bodyweight-25 milligrams over the acceptable safe intake-for six months failed to show any detectable increases in blood levels of methanol or its breakdown
Still, the science of toxicology decrees that all compounds can be potentially toxic, including salt, water and sugar. That's illustrated by another recent study that linked aspartame to various neurological side effects, such as headache, seizures and panic attacks.2 The prevailing theory is that aspartame may interfere with the sodium pump enzyme system in cells. That's significant if true, because the sodium pump regulates the entry of electrolytes in nerve cells and is vital to normal nerve function.
The study had an isolated-cell design, in which cells were exposed to varying levels of aspartame. At low exposure levels aspartame had no effect on the sodium pump mechanism. At high concentrations, though, it indeed inhibited the activity of the sodium pump, which could lead to many symptoms of electrolyte imbalance. The effect was due to increased oxidation incurred by high levels of aspartame exposure. On the other hand, the amino acid L-cysteine and glutathione completely blocked the negative effects of aspartame on the sodium pump mechanism.
L-cysteine is the nutritional precursor of glutathione, which itself consists of three amino acids and is one of the body's most vital antioxidant compounds. That may explain why you don't see more aspartame-produced side effects. First, few people ingest enough to cause toxic effects. Second, if you use such supplements as whey protein, N-acetylcysteine or lipoic acid, you're producing optimal levels of glutathione in the body.
There is little to fear from aspartame, unless you're taking in huge amounts of the sweetener. Adults would need to drink 10 cans a day of an aspartame-sweetened beverage just to get to the acceptable intake of 40 milligrams per kilogram of bodyweight per day. Most people get an average of 10 milligrams per kilogram a day. Because of its phenylalanine content, aspartame may produce problems in those born with a genetic lack of enzymes needed to process the amino acid PKU, or phenylketonuria. For them, aspartame may indeed turn bitter.
References
1 Soffritti, M., et al. (2006). First experimental demonstration of the multipotential carcinogenic effects of aspartame administered in the feed to Sprague-Dawley rats. Environ Health Perspect 114:379-385.
2 Schulpis, K., et al. (2005). The effect of L-cysteine and glutathione on inhibition of NA+, K+ ATPase activity by aspartame metabolites in human erythrocyte membrane. Eur J Clin Nutr. [Epub ahead of print].
©,2013 Jerry Brainum. Any reprinting in any type of media, including
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