We evaluated ITLN1 expression among three clinical cohorts of the Leipzig Obesity BioBank—a cross-sectional cohort comprising of 1480 people, a cohort of people with metabolically healthy or unhealthy obesity (31 insulin-sensitive, 42 insulin-resistant individuals with obesity), and a longitudinal two-step bariatric surgery cohort (n = 65). Here, ITLN1 is linked to obesity due to melanocortin 4 receptor deficiency.