The article "Branched-chain amino acids in metabolic signalling and insulin resistance" by Lynch and Adams reviews the role of branched-chain amino acids (BCAAs) in metabolic health and their potential link to insulin resistance and type 2 diabetes (T2DM). BCAAs, including leucine, isoleucine, and valine, are essential nutrients that have both direct and indirect effects on metabolism. While BCAA supplementation has been shown to have positive effects on body weight, muscle protein synthesis, and glucose homeostasis, elevated circulating levels of BCAAs are associated with poor metabolic health, including insulin resistance and T2DM. The authors discuss two main mechanisms linking increased BCAA levels to metabolic dysfunction: persistent activation of the mammalian target of rapamycin complex 1 (mTORC1) and BCAA dysmetabolism. The mTORC1 mechanism involves the activation of serine kinases S6K1 and mTORC1, which can promote insulin resistance through serine phosphorylation of insulin receptor substrate proteins. The BCAA dysmetabolism model suggests that impaired BCAA metabolism, leading to the accumulation of toxic metabolites, can cause mitochondrial dysfunction and β-cell apoptosis, contributing to insulin resistance and T2DM. The article also highlights the importance of individual and model-dependent differences in BCAA metabolism and the role of candidate genes such as *BCKDHA*, *PPM1K*, *IVD*, and *KLF15* in obesity and T2DM. Despite the controversy surrounding the role of BCAAs in metabolic disease, the authors conclude that increased BCAA levels are more likely to be a marker of impaired insulin action rather than a direct cause of metabolic dysfunction.The article "Branched-chain amino acids in metabolic signalling and insulin resistance" by Lynch and Adams reviews the role of branched-chain amino acids (BCAAs) in metabolic health and their potential link to insulin resistance and type 2 diabetes (T2DM). BCAAs, including leucine, isoleucine, and valine, are essential nutrients that have both direct and indirect effects on metabolism. While BCAA supplementation has been shown to have positive effects on body weight, muscle protein synthesis, and glucose homeostasis, elevated circulating levels of BCAAs are associated with poor metabolic health, including insulin resistance and T2DM. The authors discuss two main mechanisms linking increased BCAA levels to metabolic dysfunction: persistent activation of the mammalian target of rapamycin complex 1 (mTORC1) and BCAA dysmetabolism. The mTORC1 mechanism involves the activation of serine kinases S6K1 and mTORC1, which can promote insulin resistance through serine phosphorylation of insulin receptor substrate proteins. The BCAA dysmetabolism model suggests that impaired BCAA metabolism, leading to the accumulation of toxic metabolites, can cause mitochondrial dysfunction and β-cell apoptosis, contributing to insulin resistance and T2DM. The article also highlights the importance of individual and model-dependent differences in BCAA metabolism and the role of candidate genes such as *BCKDHA*, *PPM1K*, *IVD*, and *KLF15* in obesity and T2DM. Despite the controversy surrounding the role of BCAAs in metabolic disease, the authors conclude that increased BCAA levels are more likely to be a marker of impaired insulin action rather than a direct cause of metabolic dysfunction.