  We study the impact of quantum gravity, formulated as a quantum field theory
of the metric, on chiral symmetry in a fermionic matter sector. We specifically
address the question as to whether metric fluctuations can induce chiral
symmetry breaking and bound state formation. Our results based on the
functional Renormalization Group indicate that chiral symmetry is left intact
even at strong gravitational coupling. In particular, we find that
asymptotically safe quantum gravity where the gravitational couplings approach
a non-Gaussian fixed point generically admits universes with light fermions.
Our results thus further support quantum gravity theories built on fluctuations
of the metric field such as the asymptotic-safety scenario. A study of chiral
symmetry breaking through gravitational quantum effects may serve as a
significant benchmark test also for other quantum gravity scenarios, since a
completely broken chiral symmetry at the Planck scale would not be in
accordance with the observation of light fermions in our universe. We
demonstrate that this elementary observation already imposes constraints on a
generic UV completion of gravity.
