[en] Understanding the effects of low doses of ionizing radiation on living systems requires detailed information on electron transport in biomaterials. This, in turn, can be obtained from the wave-vector- and frequency- dependent dielectric response function of the system ε(q,ω), via the energy-loss function, lm[-1/ε(q,ω)]. This paper describes two different possible approaches to obtaining these functions, one based on the semiempirical tight-binding approximation, the other using Hedin's many-body treatment of quasiparticle states in solids. These methods are exemplified with calculations for cubic ice (as a model for cellular structured water) and transpolyacetylene. The availability of supercomputers makes the application of these techniques feasible