Considering these intriguing studies17–27 and the importance of FLVCR1 in the maintenance of tissue heme homeostasis12–16, we aimed to investigate cross-sectionally (in two cohorts) the expression of FLVCR1 according to obesity and type 2 diabetes (T2D), and longitudinally the effects of weight gain (in rats) and weight loss (bariatric surgery of morbidly obese subjects) on AT FLVCR1 mRNA levels. Here, FLVCR1 is linked to obesity due to melanocortin 4 receptor deficiency.