Savannah: Why is this disclaimer ["CONTAINS PHENYLALANINE"] on most diet sodas?

Well, for some people, it's life or death. The warning is about phenylalanine, an ingredient found in artificial sweeteners, like in sodas. It's something we can't live without, but we also can't handle too much. Phenylalanine turns into things like dopamine and adrenaline, which are - you know - pretty important. And it's in all sorts of foods, so you don't NEED artificial sweeteners to get it.

But some people have a genetic condition called PKU [phenylketonuria] that makes ingesting too much phenylalanine dangerous, so it's vital to know how much they're consuming. If you have severe PKU, you don't make the enzyme that breaks down phenylalanine after use [phenylalanine hydroxylase]. Instead, it builds up in your body and can cause all sorts of symptoms from inattension to seizures.

So that's why the disclaimer on soda tells you that there's phenylalanine inside; so people with PKU don't accidentally overload their systems.

To learn more, you can watch the full-length SciShow video about all this and more now.

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