Sex Hormone Binding Globulin (SHBG) serves to regulate the hormone estrogen. If there is an excess of estrogen circulating in the body, SHBG fills in the "parking space" where the estrogen is supposed to go. If the body needs estrogen for some reason, the SHBG will "let go" and permit the estrogen to take its designated parking space.
The only thing I know about a low level of SHBG in men is that it is a risk factor for diabetes and it're related to obesity.
Wonderingwhy, I think you need to be talking with a hormone specialist, an endocrinologist (if you're not doing that already.)