The author of a blog I read recently published a post where he wrote about his Diet Dr. Pepper addiction (a monkey that I too carry on my back) and his concerns about Aspartame poisoning. Apparently, a well meaning friend told him about the internet controversy related to whether or not the methanol generated when Aspartame breaks down is toxic.
The Preface
My initial response when I come across references to one of the many internet hysterias scuttling about the Tubes is to scoff and click on. There's so much innuendo, rumor and distorted argument out there in the Tubes that finding dependable information is well nigh impossible unless you already have a good sense of what the correct answer looks like.
Every now and then, one of these rumors pops up in a locale that's "close enough" to me that I feel comfortable (and maybe even a little obligated) to put together a well thought out counter argument. Of course, when you do that, you always run the risk of offending someone. That's why I always try very hard to not affect the "everyone else is retarded" attitude that seems to infest a lot of the Tubes. Honestly, there are an enormous number of wildly varying opinions and it can be very difficult at times to figure out who's telling the truth.
The Reference Materials
Much of this information is gathered into a single source on Snopes. The first bit of the Snopes page contains that chain email that was the "seed" material for the urban legend.
Then there's links to rebuttals. My preference is the link to a letter published in The Lancet, as its a VERY prestigious medical journal, contains a good bit of technical information and address the actual Tubes related controversy to an extent.
I also relied fairly heavily on some pages on Wikipedia. While "tube-a-pedia" can often be a powerful source for disinformation, it can also be accurate and in the instances I used it for, I think it is.
The Analysis
Aspartame is made of two amino acids (Phenylalanine and Aspartic Acid) that are held together by a "methyl ester" bond. When ingested, Aspartame is split into its constituent amino acids and a methanol molecule is released. The reaction looks like this:
Near as I can tell from a quick perusal of tube-info is that, when in solution, Aspartame is an inherently unstable molecule and the "hydrolysis" reaction is going to happen no matter what.
However, how quickly this reaction occurs is a function of both the acidity and the temperature of the environment.
In a very acidic environment (like a can of diet soda) the molecule is fairly stable and thus useable as a consumer product.
In a neutral environment (like your intestines once your stomach acid's been neutralized or your blood) the molecule is a lot less stable. So, once ingested, it's pretty good bet that some, if not all, of the Aspartame is gonna break down.
So then, we're left with methanol, phenylalanine and aspartic acid. All of these are going to get absorbed into the blood stream and either excreted via the kidneys, metabolized by the body and excreted or (gasp!!) incorporated into your bodies genetic structure!!!
"How is this possible and will I develop mutant powers?", you ask? Well no, because you see, Phenylalanine and Aspartic Acid are both amino acids. Amino acids are the molecules your body uses to make proteins, your DNA and neurotransmitters. So, ingestion of these materials is not inherently bad.
In some cases, the ingestion of a specific amino acid can be harmful if your body lacks the ability to metabolize excess molecules of that type. In the specific case of Phenylalanine, some people cannot metabolize it because their body lacks the necessary enzyme thanks to an inherited genetic defect.
This is a specific metabolic disease and does not mean that any concentration of phenylalanine in the blood is bad. Rather, it is a persistently elevated concentration of phenylalanine in the blood that can cause brain damage.
Then there's the issue of the quantity of these molecules generated by ingesting a can of diet soda. I'm just going to directly quote the letter here:
Although a 330 ml can of aspartame-sweetened soft drink will yield about 20 mg methanol, an equivalent volume of fruit juice produces 40 mg methanol, and an alcoholic beverage about 60-100 mg.Personally, I find the last sentence the most illuminating. The clinical studies they're talking about aren't rocket science. If consuming 50 mg/kg of aspartame caused elevated levels of methanol, formic acid or phenylalanine in the blood stream it would be DEAD SIMPLE to find out.
The yield of phenylalanine is about 100 mg for a can of diet soft drink, compared with 300 mg for an egg, 500 mg for a glass of milk, and 900 mg for a large hamburger (1).
Thus, the amount of phenylalanine or methanol ingested 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 50 mg/kg aspartame (equivalent to 17 cans of diet soft drink daily for a 70 kg adult)
A group of motivated graduate students could perform this study on themselves with nothing more than some syringes, basic biological laboratory glassware, a centrifuge, a high pressure liquid chromatograph and some college level knowledge.
The Conclusion
So really, that's pretty much it. The idea that you're somehow poisoning yourself by ingesting diet soda sweetened with Aspartame is pretty far fetched.
The potential liability its manufacturers and industrial users would be on the hook for if it did have toxic properties is vastly countered by the extreme ease with which a group of motivated individuals could scientifically prove the existence of these properties if they were, in fact, there. And believe me, there are a lot of motivated individuals out there with access to the actual resources needed.
If you believe that a plausible case for conspiratorial cover-up can be made, then I have a friend in Nigeria with a business proposition I want you to meet.
All this being said, there are a lot of arguments to be made against the consumption of highly processed foods like diet soda. These stem, however, from arguments related to simplicity and the consumption of limited resources. If a caffeine fix is what you need, then there are better ways to go about getting that fix than a can of Diet Dr. Pepper.
