FABP4 and Insulin resistance: Serum FGF21 levels positively correlated with adiposity, body mass index (BMI), waist circumference, waist-hip ratio, fat percentage, homeostatic model assessment for insulin resistance (HOMA-IR), triglycerides, and serum adipocyte fatty acid binding protein (A-FABP) levels, and negatively associated with serum adiponectin and high density lipoprotein (HDL) cholesterol levels (28).