Endocrine studies were performed on fertile and infertile obese men an
d compared with fertile and infertile nonobese men in order to determi
ne the independent and codependent effects of obesity and fertility st
atus on the male hypothalamic-pituitary gonadal axis. The obese infert
ile group exhibited significant endocrinologic changes as compared wit
h fertile nonobese control group which was not observed in any of the
other three groups. Serum testosterone was significantly lower. The te
stosterone/estradiol ratio was significantly lower despite a lack of s
ignificant change in serum estradiol levels. Serum steroid hormone bin
ding globulin (SHBG) was significantly lower which correlated with ele
vated bioavailability of both testosterone and estradiol in the obese
infertile group. Serum luteinizing hormone levels were no different, s
uggesting that free testosterone levels were unchanged. Obese infertil
e men exhibit endocrinologic changes that are not observed in men with
either obesity or infertility alone. Reduction of serum SHBG, total t
estosterone, and testosterone/estradiol ratio appear to be a marker of
infertility among obese men.