The investigation of variations in dielectric properties of blood based on its biochemical profile is important for determining the feasibility of developing electromagnetic non-invasive sensing systems for monitoring the levels of various metabolites in blood. In this paper, the real and imaginary parts of dielectric permittivity are measured as a function of lactate concentration in the 30-60 GHz frequency range using two different measurement techniques. The blood samples are collected from a healthy subject undergoing three different exercise modes and the dielectric properties are measured with an open-ended coaxial probe technique and a custom-made millimeter wave transmission system. Good correlation is observed in measurements from the two methods, suggesting that an increase in lactate concentration lowers the imaginary part of permittivity and thus causing higher attenuation.