Researchers at the University of Buffalo concluded that obese men have lower levels of testosterone and lower levels of biologically-active free testosterone. Testosterone levels decrease with age, but this process is exacerbated in obese men.

Obesity increases risk factors linked to low testosterone levels such as sleep apnea, insulin resistance and type 2 diabetes. Excessive adipose tissue, particularly in the stomach area, interferes with hormones that control the reproductive system and decrease sperm quality. (Diabetes Care May 2010)

A healthy diet, strength training and a proper workout regimen improve body composition and may help increase testosterone levels. If you are not motivated to train, studies like this one could probably change your mind.

Follow this link to read more on this research