OBJECTIVE: To determine changes in body composition, physical performance, metabolic and hormonal parameters induced by lifestyle counselling, resistance training and resistance training with soy protein based supplemention in middle aged males. DESIGN: Randomised controlled study consisting of resistance training without (RT-G) or with (RTS-G) a soy protein based supplement and a control group with lifestyle education only (LE-G). SUBJECTS: Forty healthy middle aged men (50-65 years, BMI 25-29.9 kg/m2). MEASUREMENTS: Changes in body weight (BW) and waist circumference (WC) were measured and body composition (BC), fat mass (FM), lean body mass (LBM) were measured by skin fold anthropometry at baseline and after 12 weeks of intervention. In addition, changes in physical fitness, metabolic and hormonal parameters (lipids, glucose, fructosamines, insulin, insulin-like growth factor-1, Leptin, human growth hormone, dehydroepiandrosterone, testosterone, hs-CRP, Il-6) were evaluated. RESULTS: Thirty-five participants completed the 12 week study. No significant changes in BW were noted although RM and WC dropped and LBM increased after training, particularly in the RTS group (FM 22.6 ± 5.5 kg to 21.2 ± 4.7 kg; LBM 68.5 ± 7.2 kg to 70.1 ± 7.4; p < 0.01). Subjects in the RTS group experienced more pronounced improvements in the strength measurements than the RT group. After the training intervention there were significant changes in hormonal and metabolic parameters as well as in glycemic control, particularly in the RTS group. CONCLUSIONS: Our data suggest that resistance training, particularly in combination with a soy protein based supplement improves body composition and metabolic function in middle aged untrained and moderately overweight males.