BDNF and obesity due to melanocortin 4 receptor deficiency: Additionally, Taha et al. revealed that BDNF levels were significantly lower in people with obesity classes II and III than in those with a normal weight (p < 0.05), and the Spearman rank correlation test revealed a statistically significant negative correlation between BMI and BDNF (R = −0.478, p < 0.01) [22].