We study the impact of galactic outflows on the properties of the intergalactic medium (IGM) at redshifts z=3 and z=2 using simulations of galaxy formation that account for strong feedback effects from galactic winds driven by supernovae and active galactic nuclei (AGN). We have performed a set of simulations with the moving mesh code AREPO evolving several volumes, each with the same initial conditions but once employing the quick Lyman-alpha technique which omits any feedback onto the diffuse gas, and the other time our most advanced physical prescription incorporated in the IllustrisTNG model. Our unique setup allows us to quantify in the most clean way how galactic outflows heat the CGM and IGM, change the density distribution of diffuse gas and its Lyman-alpha forest statistics, and distribute metals across the CGM and IGM. Our results underline the importance of accounting for galaxy formation in precision studies of the IGM.