According to Japanese legend, the those who eat the flesh of a ningyo (a Japanese version of the mermaid) gains immortality. An entire series was based on this concept, which is one of my personal favorites. As of note, despite "ningyo" being a "mermaid", in legend, they are quite monstrous looking, contrary to thinking them as humans with fish tail.
Do you think this would be true in One Piece?
- Note: I'm just making this post out of sheer interest, not really hoping Luffy or anybody would go eat Keimi or something like that.
By the way
If mermaid flesh does grant immortality, would you eat it?
- On a side note, in legend, eating mermaid flesh can sometimes be considered a curse for various reason.