Testosterone and its metabolite estradiol regulate body composition and metabolism in men. Low serum testosterone and estradiol concentrations are associated with increased visceral fat, dysglycemia, and elevated risk of type 2 diabetes (T2D). Observational data suggest that 25–50% of men with T2D exhibit low serum testosterone concentrations with normal serum gonadotropin concentrations and normal responsiveness of the hypothalamo-pituitary testicular axis, often termed functional hypogonadism. Symptoms do not distinguish between lowered testosterone and obesity and its associated co-morbidities. Short-term clinical trials of testosterone treatment demonstrate modest improvements in insulin resistance and glycemic markers. However, long-term studies, such as the Testosterone for the Treatment of Tye 2 diabetes (T4DM) trial, revealed that testosterone therapy reduced T2D risk by 40% over 2 years in men with impaired glucose tolerance, with effects mediated primarily by fat mass reduction. Glycosylated albumin concentrations improved, but HbA1c showed limited responsiveness potentially due to testosterone’s effects on hematopoiesis. Testosterone also increased lean mass and bone mineral density. The TRAVERSE and TEAAM trials highlighted inconsistencies in glycemic outcomes, reflecting differences in testosterone exposure and trial designs. Recent insights suggest optimal therapeutic benefits require serum testosterone levels ≥17 nmol/L (490 ng/dL). Future research should explore the optimal testosterone exposure, long term durability of TRT effects, effect of combination with metformin and the benefits for glycemia, muscle and skeletal mass when combined with GLP-1 receptor agonists.