We consider a class of generalized antiferromagnetic local/nonlocal interaction functionals in general dimension, where a short range attractive term of perimeter type competes with a long range repulsive term characterized by a reflection positive power law kernel. Breaking of symmetry with respect to coordinate permutations and pattern formation for functionals in this class have been shown in [GR19; DR19b] and previously by [GS16] in the discrete setting, for a smaller range of exponents. Global minimizers of such functionals have been proved in [DR19b] to be given by periodic stripes of volume density 1/2 in any cube having optimal period size, also in the large volume limit. In this paper we study the minimization problem with arbitrarily prescribed volume constraint α ∈ (0, 1). We show that, in the large volume limit, minimizers are periodic stripes of volume density α, namely stripes whose one-dimensional slices in the direction orthogonal to their boundary are simple periodic with volume density α in each period. Results of this type in the one-dimensional setting, where no symmetry breaking occurs, have been previously obtained in [Mül93; AM01; RW03; CO05; GLL09].