MC4R and obesity due to melanocortin 4 receptor deficiency: We and others have shown that SG is not effective in maintaining weight loss in early-onset genetic obesity modeled by db/db mice or Melanocortin 4 Receptor null rats, yet it is effective in obesity models induced through a calorie-rich diet (Hatoum et al., 2012; Abu-Gazala et al., 2018; Ben-Haroush Schyr et al., 2021).