  The density response function $N(q,\omega)$ of the two-dimensional $t-J$
model is studied starting from a mixed gauge formulation of the slave boson
approach. Our results for $N(q, \omega)$ are in remarkable agreement with exact
diagonalization studies, and provide a natural explanation of the anomalous
features in the density response in terms of the spin polaron nature of the
charge carriers. In particular we have identified unexplained low energy
structures in the diagonalization data as arising from the coherent polaron
motion of holes in a spin liquid.
