A meta-analysis by Gao Z et al. demonstrated a significant reduction in fasting GIP levels after Roux-en-Y gastric bypass (RYGB) in individuals with obesity (SMD = 0.38, 95% CI: 0.21 to 0.56, p < 0.0001) [106]. Here, GIP is linked to obesity due to melanocortin 4 receptor deficiency.