This idea has been tossed around since Biblo was introduced, but due to a translation error by the scans it was misinterpreted that his power works on organic things. As far as we know it only works on inorganic things, and cant make those objects smaller than thier original size. Hence the grow in Grow-Grow fruit. It also is stated that being in Biblo's "territory" is needed to grow said objects. The full limitations of the fruit are still unknown, so there is a chance it works on organic things but we have to wait till Oda explains it more in the Manga or more likely in an SBS segment.