GPT and metabolic syndrome: GGT - gamma-glutamyl transferase; BMI - body mass index; AST - aspartate transaminase; ALT - alanine transaminase; TG - triglycerides; WC- waist circumference; WHR - waist-to-hip ratio; HOMA - homeostatic model assessment; MetS - metabolic syndrome; DM - diabetes mellitus; T2DM - type 2 diabetes mellitus; FSI - fasting serum insulin