2010 Meta Analysis: The impact of body mass index on semen parameters and reproductive hormones in human males: a systematic review with meta-analysis.
There was strong evidence of a negative relationship for testosterone, SHBG and free testosterone with increased BMI.

2013 Study: Body mass index in relation to semen quality and reproductive hormones in New Zealand men: a cross-sectional study in fertility clinics.
Of the reproductive hormones, significant negative relationships with BMI were found for total testosterone (r = -0.35, P = <0.0001), free testosterone (r = -0.25, P = <0.0012) and SHBG (r = -0.44, P = <0.0001).