Short-Term Estrogen Withdrawal Increases Adiposity in Healthy Men.

Abstract

T deprivation increases risk of insulin resistance in men, but whether this risk is independent of changes in body composition is unknown. Further, the metabolic roles of T and its metabolite estradiol have not been clearly defined in men. This study sought to establish the effects of selective sex steroid withdrawal on insulin sensitivity in healthy men. This was a double-blinded, placebo-controlled, randomized trial at an academic medical center of 56 healthy men, 19-55 years of age. Subjects received the GnRH antagonist acyline plus one of the following: placebo gel (Castrate), 1.25 g testosterone gel (Low T/E), 5 g testosterone gel (Normal T/E), or 5 g testosterone gel with letrozole (Normal T/Low E) daily for 4 weeks. Body composition and glucose tolerance were assessed at baseline and end of treatment. Insulin sensitivity was quantified by the Matsuda index. Predicted circulating sex steroid concentrations were achieved in all treatment groups. The time-by-group interaction for Matsuda index did not achieve significance in overall repeated measures ANOVA (baseline vs week 4; P = .16). A significant time-by-group interaction was observed for fat mass (P = .003), with changes in fat mass attributable predominantly to estrogen exposure in linear regression analysis (P = .016). A time-by-group interaction also was observed for lean mass (P = .03) and influenced by androgen exposure (P = .003). Short-term sex steroid withdrawal in healthy men causes adverse changes in body composition. These findings support the role of estradiol as a determinant of adiposity in men.