  Motivated by string/M-theory predictions that scalar field couplings with the
Gauss-Bonnet invariant, G, are essential in the appearance of non-singular
early time cosmologies, we discuss the viability of an interesting alternative
gravitational theory, namely, modified Gauss-Bonnet gravity, and present the
viability bounds arising from the energy conditions. In particular, we consider
a specific realistic form of f(G) analyzed in the literature that accounts for
the late-time cosmic acceleration and that has been found to cure the
finite-time future singularities present in the dark energy models, and further
examine the respective viability of the specific f(G) model imposed by the weak
energy condition.
