The artificial sweetener aspartame is a food ingredient that is perhaps the most controversial of all: Its manufacturers and official bodies claim it's safe, but a stack of anecdotal evidence and a fair degree of science says it's not.
Tellingly, whether a study finds for or against aspartame seems to be intimately related to, er ... who paid for it. One online review  of the evidence finds that while 100 percent of industry-funded studies conclude aspartame is safe, 92 percent of independently funded research and reports identified aspartame as a potential cause of harmful effects.
In a review published this month in the European Journal of Clinical Nutrition, scientists in South Africa assessed the potential effects not just of one of aspartame's components, methanol, but other constituents (phenylalanine and aspartic acid) on the brain. The review is long and detailed and is supported by more than 50 scientific references.
In their review of the effects of phenylalanine, the authors detail the ability of this chemical to disrupt the chemistry of the brain, including its potential to lower levels of key brain chemicals such as serotonin (which may adversely influence all sorts of things including mood, behavior, sleep, and appetite).
The authors note that phenylalanine also has the potential to disrupt amino acid metabolism, nerve function, and hormonal balance in the body. They go on to suggest that aspartame has the ability to destroy nerve cells and that this damage may mimic or even cause Alzheimer's disease.
When the authors of this review turn their attention to aspartic acid, they highlight this chemical's ability to stimulate or 'excite' the nervous system.
In their analysis of the effect of methanol in the body, the authors describe the ability of this substance to create formaldehyde, along with the cancer-causing agent diketopiperazine and a "number of highly toxic derivatives."
Here are the conclusions that come at the end of this review  (I've added some detail in brackets here and there to aid clarity and understanding):
"It was seen that aspartame disturbs amino acid metabolism, protein structure and metabolism, integrity of nucleic acids [which are the building blocks of DNA], neuronal function, endocrine [hormonal] balances, and changes in the brain concentrations of catecholamines [brain chemicals such as noradrenaline and dopamine that can affect, among other things, mood].
"It was also reported that aspartame and its breakdown products cause nerves to fire excessively, which indirectly causes a very high rate of neuron depolarization [which basically means aspartame has the capacity to 'excite' nerve cells].
"The energy systems for certain required enzyme reactions become compromised, thus indirectly leading to the inability of enzymes to function optimally.
"The ATP [the basic currency for energy in the body] stores in the cells are depleted, indicating that low concentrations of glucose are present in the cells, and this in turn will indirectly decrease the synthesis of acetylcholine, glutamate, and GABA [chemicals that play a part in nerve and brain function].
"The intracellular calcium uptake has been altered, thus the functioning of glutamate as an excitatory neurotransmitter is inhibited.
"Mitochondria [the miniature 'engines' that generate energy in the body's cells] are damaged, which could lead to apoptosis of cells and infertility in men and also a lowered rate of oxidative metabolism are present, thus lowering concentrations of the transmitters glutamate and production of GABA.
"The cellular walls are destroyed; thus, the cells [endothelium of the capillaries] are more permeable, leading to a compromised BBB [the 'blood brain barrier'—a structure which, in health, keeps certain substances from making their way from the blood stream into the brain]. Thus, overall oxidative stress and neurodegeneration are present.
"From all the adverse effects caused by this product, it is suggested that serious further testing and research be undertaken to eliminate any and all controversies surrounding this product."
If you read this study in full (or even this short summary of it), it's difficult not to come away with the idea that aspartame has considerable potential for harm. The best thing, I think, would be for this substance to be banned from the diet. At the very least, I'd like to see the potential problems with aspartame to be widely known, so individuals can at least make a properly informed decision about whether to consume it or not. Here's hoping that this latest review of aspartame gets the publicity it deserves.
Editor's Note: Equal® and NutraSweet® are two brands of aspartame.
 Humphries P, et al. Direct and indirect cellular effects of aspartame on the brain European Journal of Clinical Nutrition 2008; 62:451–462
Dr. John Briffa is a London-based doctor and author with an interest in nutrition and natural medicine.
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