During the 1990s, research out of Japan found that steviosides, the “active” ingredient in stevia, appeared harmless. But in the guts of rats, intestinal bacteria transformed steviosides into a toxic substance called steviol, which can cause a big spike in mutagenic DNA damage in vitro.88 Unfortunately, it turns out that humans have the same bacterial activity in their guts.89 It’s the dose that makes the poison, though.
