  We study some properties of a dimensional reduction mechanism for fermions in
an odd number D+1 of spacetime dimensions. A fermionic field is equipped with a
mass term with domain wall like defects along one of the spacelike dimensions,
which is moreover compactified. We show that there is a regime such that the
only relevant degrees of freedom are massless fermionic fields in D dimensions.
For any fixed gauge field configuration, the extra modes may be decoupled,
since they can be made arbitrarily heavy. This decoupling combines the usual
Kaluza-Klein one, due to the compactification, with a mass enhancement for the
non-zero modes provided by the domain wall mechanism. We obtain quantitative
results on the contribution of the massive modes in the cases D=2 and D=4.
