Fatty acid-binding protein 4 (FABP4), abundantly produced by adipocytes, is released under lipolytic conditions and has been shown to enhance hepatic gluconeogenesis; in obesity and T2DM, circulating FABP4 levels are elevated, yet Mendelian randomization suggests no direct causal impact on insulin resistance [216,219,220]. Here, FABP4 is linked to obesity due to melanocortin 4 receptor deficiency.