We found that growth-regulated alpha protein (GROA) (BMI: OR = 0.9929, 95% CI [0.9868–0.9990], P = 0.0236; Obesity class 1: OR = 0.9506, 95% CI [0.9067–0.9965], P = 0.0354) was the only shared causal cytokine that could reduce the risk of obesity. This evidence concerns the gene CXCL1 and obesity due to melanocortin 4 receptor deficiency.