[ghostzilla]

It is the statistical processes that determine how much something is "natural". Our bodies evolved alongside fruit that was on the smaller and less sweet side, and logically that's what we are the most compatible with. Over centuries and millennia we selected fruits to favor size and sweetness, and over 5 years we e.g. genetically modify a strawberry to have peach flavor. The last one is like a step function compared to the slow moving processes of the agricultural selection and so less "natural" and almost certainly less compatible with our bodies.

We might still get lucky and get beneficial side effects of aspartame or peach-flavored strawberries that makes us faster, stronger, smarter, but with these things the luck usually works in the other direction.