  We calculate isolated photon production at forward rapidities in
proton-nucleus collisions in the Color Glass Condensate framework. Our
calculation uses dipole cross sections solved from the running coupling
Balitsky-Kovchegov equation with an initial condition fit to deep inelastic
scattering data and extended to nuclei with an optical Glauber procedure that
introduces no additional parameters beyond the basic nuclear geometry. We
present predictions for future forward RHIC and LHC measurements. The
predictions are also compared to updated results for the nuclear modification
factors for pion production, Drell-Yan dileptons and $J/\psi$ mesons in the
same forward kinematics, consistently calculated in the same theoretical
framework. We find that leading order, running coupling high energy evolution
in the CGC picture leads to a significant nuclear suppression at forward
rapidities. This nuclear suppression is stronger for photons than for pions. We
also discuss how this might change with next-to-leading order high energy
evolution.
