Bioelectrical impedance analysis measures the impedance to flow of an alternating electrical current passed through biological tissue. Such impedance measurements allow one to estimate fat-free body mass which is an accepted estimate for lean body weight, considered by some to be a better predictor of drug clearance in the obese than, for example, total body weight. D-optimal designs for nonlinear mixed effects bioimpedance models are explored. Despite the wide use of such models in this area, it is well-known that they have poor predictive performance at extreme frequencies. D-optimal designs that account for this variation, and also possible misspecification of initial parameter estimates, are found in an attempt to form practical and applicable designs.