Cross-sectional evidence in humans shows a negative gradient relationship between body mass index (BMI), glycemic control, and plasma BDNF such that lean, normoglycemic individuals had the highest plasma BDNF and people with obesity and type 2 diabetes (T2D) had the lowest (Krabbe et al., 2007). This evidence concerns the gene BDNF and obesity due to melanocortin 4 receptor deficiency.