MTOR and obesity due to melanocortin 4 receptor deficiency: Among them, the branched chain amino acids (BCAAs) refer to leucine (Leu), isoleucine (Ile), and valine (Val), and are important nutrition signals that have important mediation effects on protein synthesis, glucose homeostasis, anti-obesity, and nutrient-sensitive signaling pathways, e.g., phosphoinositide 3-kinase-protein kinase B (PI3K-AKT), mammalian target of rapamycin (mTOR) [1,2].