The latest research on this topic is quite conclusive, testosterone concentrations, in males particularly, correlate with body composition. That means low testosterone levels are linked strongly to fat accumulation and vice-versa. However, not all testosterone is the same. Testosterone bound to protein (serum binding globulin, or SHBG) doesn’t work as well as free testosterone for stimulating protein synthesis in muscle cells to pack on mass.
Men over 30 years of age show a gradual decline in blood free testosterone and an increase in SHBG. To concur with this, older men show an age-related decline in muscle mass and an accumulation of body fat. However, the big question is, dose testosterone decrease body fat by itself or by other factors such as improving the way insulin affects carbohydrate or fat metabolism?
Scientists are still a long way off answering this question, but researchers from the University of Texas Southwestern Medical Center have discovered that levels of SHBG in men are a good indicator of body fat levels. Based on their findings, it seems as though men should do all they can throughout life to maintain optimal testosterone production.
Men who lift weights regularly and intensely, always enjoy higher testosterone levels than their peers who perform other forms of exercise. Quite a few studies reveal that intense weight lifting maintains and even enhances natural testosterone production throughout life. Men who commit themselves to pumping iron for life can experience testosterone levels similar to those seen in untrained young men.