BDNF and obesity due to melanocortin 4 receptor deficiency: Figure 1 depicts the correlation between BDNF levels and food cue-reactivity in the left and right insula in patients suffering from obesity (rLeft = 0.705, p < 0.001; rRight = 0.536, p = 0.009) and in non-obese group (rLeft = − 0.534, p = 0.008; rRight = − 0.595, p = 0.003).