It is shown that baryon chiral perturbation theory can be employed to calculate the excited-state contamination in various nucleon observables due to two-particle nucleon-pion states. Leading order results are presented for the nucleon axial, tensor and scalar charge and three Mellin moments of parton distribution functions (quark momentum fraction, helicity and transversity moment). Taking into account phenomenological results for some charges and moments the impact of the nucleon-pion-states on the plateau estimates for these observables can be estimated. The nucleon-pion-state contribution results in an overestimation of all charges and moments in lattice simulations. In physical point simulations the overestimation is at the 5-10% level for source-sink separations of about 2 fm.