Several studies have suggested that the serum level of bilirubin is inversely linked with many health conditions such as obesity, metabolic syndrome, T2D, and oxidative stress-mediated diseases due to the increase in the glucuronic UGT1A1 enzyme in the liver among obese subjects that can clear bilirubin from the blood [46,47]. Here, UGT1A1 is linked to obesity due to melanocortin 4 receptor deficiency.