Interesting. You'd think we would have heard more about it being a major complaint and all. What "by-products" are you referring to and why wouldn't the liver be able to clear them just like the same amino acids and methanol from natural sources?
What percent of the population is at some point in their lives likely to inadequately clear the break-down products of aspartame
First, you're going to have to establish what you mean by break-down products? It appears that you're making an assumption that the components of aspartame create a "build up" of "by-products" while phenylalanine, aspartic acid and methanol from natural sources do not. Sounds like quite a story to me but I'll reserve judgment until you define your terms better.
It may be that the essential amino acids have to be consumed in a balanced mixture.
If you want a complete protein they do. In the case of aspartame, your gut breaks down aspartame into the individual amino acids before they are cleared by the liver. Your gut also breaks down long chains of amino acids into individual amino acids before they are absorbed and cleared by the liver. There are some small peptides that don't break down but most are individual.
Still, I want to thank you for inspiring me to look things up. As you could. And the wee little mosguito-like Toddster could as well.
What are the best arguments of your opponents, in their view?