[Kransha]

To shed some light on the subject.
I believe that there may not be giants per se, since they were originally intended as a plot driving symbol. In one of Tolkein's writings (I don't remember which), Tolkein talks about the flora and fauna of Arda in excess. He does not denote giants as fauna and in fact adds a side note saying that he did so for a reason. The giants, he says, who were encountered in the Hobbit, were a technical metaphor for thunder, possibly not physical beings. He said it was up to the reader to decide whether they were real or not, and if they decided upon the existence of giants, he had nothing to back that opinion up.