User blog comment:LuffyPirateKing/Luffy and his belly/@comment-1595565-20121021173205/@comment-3119203-20121021195802

Are you suggesting that any Logia user can therefore eat another Devil Fruit because their bodies will patch themselves up when they're done? My idea was that Blackbeard didn't eat the fruit directly, but merely absorbed its powers (maybe the Yami Yami no Mi issuppressing the power of the Gura Gura no Mi?), which is why he didn't blow up. Luffy on the other hand, can only intake fruits by eating them, which kind of cancels out that possibility. If he can find some way to absorb another DF (like the weapon-DF thing) then yes, I think he could use both of them.

This is mainly based on theory. I am a believer in the idea that Devil Fruits have spiritual manifestations that can move from fruit to body and from body to fruit after the body dies (this idea was actually part of DP's Devil Fruit blog....), so this makes sense to me right now.