LEP and type 2 diabetes mellitus: It is widely accepted that men with type 2 diabetes (T2D) tend to have lower testosterone levels than the general population [1] Reduced testosterone levels are associated with reduced insulin sensitivity, i.e., insulin resistance in men with T2D [2,3] Previous studies have suggested that low testosterone levels are related to insulin resistance and elevated leptin levels in patients with T2D, especially in those with obesity [4,5].