The energy straggling of protons and helium ions is investigated based on the dielectric function theory of Lindhard and Winther using two local electron density models (LEDM). Not only point charges (H +, He 2+), but also a partially stripped ion (He +), are treated. At low energies, the collisional straggling of point charges is proportional to the energy, and at high energies it approaches the value predicted by Bohr. The solid LEDM calculation yields larger straggling values than the atomic LEDM does. The straggling due to change state fluctuations of a 250 keV/amu helium beam results in an enhancement of the well-known Z2 (target atomic number)-oscillation.