Low levels of testosterone, free testosterone and increased levels of serum hormone binding globulin boost the risk of obesity.

Testosterone supplements reduce body fat, particularly in the abdomen, in hypogonadal men (men with low testosterone levels) and in aging men.

A literature review by Caroline Allen and Robert MacLaughlin concluded that low testosterone and aging increase the risk of obesity.  We need more research to determine the effects of testosterone supplements in men who are moderately overweight.  Lifestyle factors such as caloric restriction and physical activity are more important than low testosterone levels in promoting weight loss and preventing obesity in aging men.  (Current Opinion in Endocrinology, Diabetes and obesity: 17: 224-232, 2010)