The long-term influences of sex hormone administration on insulin sensitivity and incretin hormones are controversial. We investigated these effects in 35 transgender men (TM) and 55 transgender women (TW) from the European Network for the Investigation of Gender Incongruence (ENIGI) study. RESEARCH DESIGN AND METHODSBefore and after 1 year of gender-affirming hormone therapy, body composition and oral glucose tolerance tests (OGTTs) were evaluated. RESULTSIn TM, body weight (2.8 6 1.0 kg; P < 0.01), fat-free mass (FFM) (3.1 6 0.9 kg; P < 0.01), and waist-to-hip ratio (20.03 6 0.01; P < 0.01) increased. Fasting insulin (21.4 6 0.8 mU/L; P 5 0.08) and HOMA of insulin resistance (HOMA-IR) (2.2 6 0.3 vs. 1.8 6 0.2; P 5 0.06) tended to decrease, whereas fasting glucose (21.6 6 1.6 mg/dL), glucose-dependent insulinotropic polypeptide (GIP) (21.8 6 1.0 pmol/L), and glucagon-like peptide 1 (GLP-1) (20.2 6 1.1 pmol/L) were statistically unchanged. Post-OGTT areas under the curve (AUCs) for GIP (2,068 6 1,134 vs. 2,645 6 1,248 [pmol/L] 3 min; P < 0.01) and GLP-1 (2,352 6 796 vs. 2,712 6 1,015 [pmol/L] 3 min; P < 0.01) increased. In TW, body weight tended to increase (1.4 6 0.8 kg; P 5 0.07) with decreasing FFM (22.3 6 0.4 kg; P < 0.01) and waist-to-hip ratio (20.03 6 0.01;

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