Blood is a pH buffered solution, and the average adult has around 5 liters of it. A standard can of diet coke has approximately 200mg of aspartame, 10% of which is metabolised to methanol. That 20mg of methanol is metabolised rapidly by alcohol dehydrogenase into formaldehyde. This formaldehyde is then rapidly metabolised into formic acid via formaldehyde dehydrogenase – alcohol dehydrogenase is the rate limiting step in this process. By and large, the pathological effects of methanol are related to metabolic acidosis (a drop in blood pH) from build-up of formic acid.
I’ve been messing around with the chemistry for an hour or so, but am way too out of practice to write anything sensible about it. So for now, I’m going to go with the following bits and pieces I’ve found out:
- The lowest recorded fatal dose of methanol is 6 grams. That’s 300 times the amount of methanol produced by the metabolism of one can’s worth of aspartame.
- Methanol is metabolised with a half-life of around 1.5 to 2 hours in humans at levels found in artifically sweetened drinks, fruit juices and red wine.
- A glass of tomato juice contains enough pectin to produce approximately 85mg of methanol during metabolism – as compared to apple juice (21mg) and diet coke (20mg).
Draw whatever conclusions you like from that. Perhaps when I’ve got a bit more free time I might have another stab at calculating the ability of blood to buffer the formic acid. If you feel like having a stab, here’s a journal article outlining the buffering capacity of human blood.
Oh and check out this article too, on aspartame metabolism relating directly to methanol production.