This article presents data related to the research article entitled Considerations for readdressing theoretical descriptions of particle-filled composite food gels [1]. The elastic modulus of mixed biopolymer composite gels consisting of heat-set whey protein isolate and xanthan gum (WPI-X) filled with glass microspheres is reported. Gels were evaluated as a function of volume fraction filler (φf = 0-0.5), with varying filler size (4 μm, 7-10 μm, 45-90 μm, and 150-210 μm) and ionic strength of the protein phase (0, 50, 100, 200 mM NaCl). The reported elastic modulus data was extracted from large deformation uniaxial compression tests. This data is relevant to the development of alternative particle reinforcement models, or adaptation of existing theories. Further, it represents the limiting case of rigid inclusions, which can eliminate certain confounding assumptions in established models.