I've been warning patients about the potential problems associated with Nutrasweet/Equal/Aspartame for years. While I no longer consume aspartame (and feel better for it) and encourage patients with chronic health problems to stop using it (and their health problems often improve) there are nonetheless many people who can consume aspartame regularly and who seem to suffer no apparent ill effects. My explanation for this is that there are probably genetic, biochemical, and enzymatic differences from person to person that affect how aspartame and its toxic metabolites are handled. While I think there are good reasons to ban the production and sale of aspartame I also think that alarmist, overstated and distorted claims about aspartame being the evil root of all health problems are actually counterproductive and make reasonable people turn a deaf ear to this important public health issue. If you personally are a victim of aspartame toxicity it is hard to maintain objectivity and not become alarmist and overstate the issue (thus losing credibility) to the detriment of your long term cause - which is to have aspartame banned so that others don't have to suffer the same problems. Remember there are many people who can consume aspartame without apparent ill effects. In the end the truth about the potential health risks of aspartame will become widely known and people will avoid it even if the government agencies don't do the right thing and ban its use. 

Enough philosophizing, what are the facts about aspartame? Aspartame is metabolized to aspartic acid, phenylalanine and methanol (wood alcohol). Methanol is toxic. The manufacturers of aspartame claim that the amounts of methanol in foods or drinks sweetened with aspartame are not enough to cause toxicity. They further state that we are routinely exposed to larger amounts of naturally occurring methanol in foods. The problem with this argument is that some people do in fact consume very large quantities of aspartame when you add up the several diet sodas, the sugar free yogurt, the sugar free cereal, the sugar free Jello, the sugar free pastries, the sugar free gum and lozenges, etc. that they consume on a daily basis. Also because of genetic, biochemical, enzymatic variability some people can handle much less methanol without toxicity. As far as the naturally occurring methanol in foods, there are in those same foods substances which tend to counteract or attenuate the toxic effects of methanol. The same cannot be said of aspartame. 

Methanol is metabolized to formaldehyde. Formaldehyde is generally best avoided unless you are trying to embalm yourself. Formaldehyde is in turn metabolized to formic acid which is what you feel when a fire ant stings you. Formic acid is what causes optic nerve damage and can even cause blindness. Since optic nerve inflammation (optic neuritis) is often seen in multiple sclerosis, patients with optic neuritis from aspartame consumption may be inappropriately diagnosed and treated for multiple sclerosis when in fact they simply need to quit consuming aspartame. The converse side of this is that there are patients who develop multiple sclerosis in which aspartame consumption has played no role whatsoever. 

Aside from the toxicity associated with methanol. Aspartic acid and phenylalanine are not totally benign. Excluding those individuals who have PKU (phenylketonuria - a genetic inability to dispose of the amino acid phenylalanine quickly enough) consumption of aspartame can cause significant changes in blood and brain chemistry. Consumption of a diet soda between meals means that the blood levels of both aspartic acid and phenylalanine will rise disproportionately compared to other amino acids in the blood (this is not the case when consuming protein which has a balanced blend of amino acids). The disproportionate rise in blood levels of aspartic acid and phenylalanine results in more of these amino acids being transported across the blood brain barrier which in turn leads to elevated levels of these substances in the brain. The result is over stimulation and potentially damage of neurons (nerve cells). The other thing that happens when aspartic acid and phenylalanine levels go up in the brain is that serotonin levels go down. This change in brain serotonin levels predisposes people to a variety of problems including depression, headaches, sleep disorders, eating disorders and fatigue to name a few. 

The bottom line with aspartame is that some people clearly have problems with it and some people don't seem to have problems. We understand how aspartame is metabolized and can explain on a biochemical and physiologic basis how aspartame can cause health problems. What we don't know yet is how to genetically or biochemically identify those of us who are more susceptible to aspartame toxicity and those who are less susceptible. Until we are able to distinguish between those who are "aspartame vulnerable" and those who are "aspartame resistant" I think it is prudent to avoid consuming aspartame. For those who have chronic health problems that have not responded to other interventions a trial of avoiding aspartame for several months may produce noticeable benefits. For those without health problems who have a hard time giving up aspartame I would recommend consuming it only with meals that have protein to offset any negative biochemical effects. I would totally avoid aspartame during pregnancy.

For those interested in reading more about aspartame toxicity I would recommend the following books: - Aspartame (Nutrasweet : Is It Safe?) by Hyman Jacob Roberts and H. L. Roberts. - Excitotoxins : The Taste That Kills by Russell L. Blaylock