Electron energy loss spectroscopy is a method of choice for the characterization of both the spatial and spectral properties of localized surface plasmon resonances. The energy lost by the impinging electrons is commonly explained by the Lorentz force acting on their motion. Here, we adopt another point of view to compute the electron energy loss spectra. Coupling the energy conservation law with full-wave electromagnetic computations based on a surface integral equation method, we derive the electron energy loss spectra directly from two dissipative processes, namely, absorption and scattering. This antenna-based approach is applied to nanostructures with different sizes and materials, showing an excellent agreement with experimental observation and computations based on the evaluation of the Lorentz force. This formalism permits the easy separation of absorption losses in the nanostructures forming a coupled system and reveals the subtle interplay between absorption and scattering, which are controlled by the materials, the nanostructure size, and the energy range.