Increased testosterone can have an impact on body composition. Possible benefits include gains in lean muscle mass, reduced body fat and increased bone density. Testosterone inhibits uptake of triglycerides and increases lipid mobilization from adipose tissue, and the increase or decrease of testosterone will usually have an inverse effect on fat stores, with higher testosterone generally causing a decrease in body fat. "The Journal of Clinical Endocrinology and Metabolism" published a study in 2007 that showed decreases in body fat and increases in lean mass in HIV-positive obese men given testosterone therapy. In 1989, a study of the effects of testosterone on muscle mass at the University of Rochester School of Medicine and Dentistry suggests that increasing testosterone increases protein synthesis in muscles. Body composition changes from increased testosterone were also demonstrated in a 1999 study at the School of Exercise Science and Sports Management, Southern Cross University in Australia performed on male weight-training subjects, which showed increases in arm girth and body weight and decreased body fat following a 12-week cycle of testosterone enanthate.
Some of these signs and symptoms can be caused by various underlying factors, including medication side effects, obstructive sleep apnea, thyroid problems, diabetes and depression. It's also possible that these conditions may be the cause of low testosterone levels, and treatment of these problems may cause testosterone levels to rise. A blood test is the only way to diagnose a low testosterone level.