One of my readers has forwarded an e-mail purporting to warn of the dangers of so-called aspartame poisoning. This particular e-mail has been circulating since at least 1998 & has been eviscerated on sites such as the hoax-busting Snopes.com, but I thought I might address some of its wilder claims here anyway (I feel like something 'lighter' today!).
Now, before we get started, there is one sector of the population that does have to avoid foods & drinks that contain aspartame, and that's people who suffer from the genetic disorder phenylketonuria (PKU). Most people have an enzyme called phenylalanine hydroxylase, which changes phenylalanine into tyrosine, another amino acid. Individuals with PKU partially or completely lack this enzyme & so phenylalanine (& the breakdown products produced by other enzymes) builds up in their bodies. In high concentrations this can cause major neurological problems if left untreated - this is why newborn infants are tested for this disorder.
Anyway, back to that e-mail. The author (or possible author; these things are cut-&-pasted so often that it's hard to tell) says they'll explain why the commonly-used sweetener aspartame is so dangerous:
When the temperature of this sweetener exceeds 86 degrees F, the wood alchohol in aspartame converts to formaldehyde and then to formic acid, which in turn causes metabolic acidosis. Formic acid is the poison found in the sting of fire ants. The methanol toxicity mimics, among other conditions, multiple sclerosis and systemic lupus.
In addition to the use of scare tactics (formic acid is poison! Oh noes!), this displays a lack of understanding of human physiology - & also of the concept of dosage. Anthony Zehetner & Mark McLean responded to this one back in 1999. Writing in The Lancet, they began by describing what happens to aspartame when it's ingested. Aspartame is what's known as a 'dipeptide': it's made up of 2 amino acids (phenylalanine & aspartic acid), here joined together by a methyl ester bond. When it hits your intestine it's digested - like any other di- or polypeptide - into the separate amino acids, plus methanol (this is the letter-writer's 'wood alcohol'). It's this methanol and the phenylalanine that are supposed to be so bad for us.
Now, quite apart from the fact that our own bodies produce methanol (e.g. after eating fruit) and formaldehyde as part of normal physiological processes, the amounts produced are important here. Zehetner & McLean state that
[although] a 330mL can of aspartame-sweetened soft drink will yield about 20mg methanol, an equivalent volume of fruit juice produces 40mg methanol, and an alcoholic beverage about 60-100mg. The yield of phenylalanine is about 100mg for a can of diet soft drink, compared with 300mg for an egg, 500mg for a glass of milk, and 900mg for a large hamburger. Thus, the amount of phenylalanine or methanol [gained] from consumption of aspartame is trivial, compared with other dietary sources. Clinical studies have shown no evidence of toxic effects and no increase in plasma concentrations of methanol, formic acid, or phenylalanine with daily consumption of 50mg/kg aspartame (equivalent to 17 cans of diet soft drink daily for a 70kg adult).
Given those figures, then to be consistent surely the author of the original e-mail should be railing against the eating of hamburgers and drinking of wine?
What about the claim that methanol toxicity (however caused) 'mimics' the symptoms of lupus (lupus erythematosus, an autoimmune disease)? Medscape tells us that while those who've ingested too much methanol initially appear drunk, they can go on to develop 'headaches, nausea, vomiting' or stomach pains before becoming sleepy (from which they may rapidly enter a coma). Patients may also become blind, due to the effects of formic acid on the optic nerve (yes, formic acid is toxic - in large enough amounts).
Lupus, on the other hand, is characterised by sore & swollen joints, maybe accompanied by arthritis. Patients my also commonly experience chest pain, fatigue, fever, hair loss, sensitivity to sunlight, swollen glands, & in about 50% of patients a 'butterfly' rash. Other symptoms depend on which part of the body is affected: brain, intestines, heart, kidneys, lungs, or skin. While both may (in some patients) have vomiting, nausea & headaches in common, these symptoms are shared with so many other disorders that it's a bit of a stretch to say that one 'mimics' the other.
Casting a critical eye over the e-mail highlights other points that suggest its claims should be taken with a grain of salt (or maybe that should be sugar?). Claims are vague & not supported by evidence or references:
We have seen patients with systemic lupus become asymptotic, once taken off diet sodas
we've seen many cases [of multiple sclerosis] where vision loss re turned [sic] and hearing loss improved markedly.
Again, who is 'we'? And where are the data? If this simple dietary change genuinely had the effects claimed for it, and could be backed up with data, then that would be well worth publishing and - if replicated by other workers - would enter the mainstream. The 12+ years since this story first began circulating would surely provide ample time for such research to be done...
Like Zehetner & McLean in The Lancet, I seriously wonder why there is such a proliferation of pseudoscientiic claims: this stuff on aspartame; the so-called 'miracle mineral supplement'; the erroneous idea that vaccination is linked to autism. Do people have such a distrust of science & science-based medicine that they find these alternatives acceptable? Are we really doing such a bad job of communicating about science & how science works?
Zehetner, A. & McLean, M. (1998) Aspartame and the internet. The Lancet 354 (9172): 78