We present a detailed energy loss characterization of natural diamond and diamond films grown on non-scratched Si substrates by the hot-filament chemical vapor deposition technique (with the help of a SiC buffer layer). The energy loss experiments were performed in a transmission electron microscope (TEM) with a GATAN-666 parallel electron energy loss spectrometer (PEELS) attachment Diamond particles are in the 0.5-1 mu m size range as observed by TEM. PEELS spectra show that the plasmon and carbon K-edge main features are very similar (in position and shapes) in both natural and our diamond film. The radial distribution function around the carbon atoms was obtained through the Fourier transform of the extended fine structure located in a 300 eV range beyond the carbon K-edge in the energy loss spectra. The values obtained for the C-C distances are very close (within 0.003 nm) to those of natural cubic diamond structure. These results confirm the good quality of the diamond films produced by our experimental technique.