Branched-chain amino acids (BCAAs) are essential nutrients that influence metabolic processes and are linked to insulin resistance and type 2 diabetes (T2DM). While BCAA supplementation is often associated with benefits for weight regulation, muscle protein synthesis, and glucose homeostasis, elevated BCAA levels are associated with metabolic dysfunction, insulin resistance, and T2DM. The mechanisms linking BCAA levels to these conditions involve mTORC1 activation, which disrupts insulin signaling, and BCAA dysmetabolism, which leads to mitochondrial dysfunction and β-cell apoptosis. BCAA dysmetabolism is characterized by the accumulation of toxic metabolites, not BCAAs themselves, which contribute to metabolic syndrome and T2DM. Studies suggest that BCAA levels are influenced by factors such as protein degradation, mitochondrial function, and gene expression. Genes like BCKDHA, PPM1K, IVD, and KLF15 are associated with obesity and T2DM. BCAA metabolism is affected in obesity and T2DM, with altered enzyme activity and increased BCAA-related acylcarnitines. The role of BCAA metabolism in these conditions remains complex, with both mTORC1 activation and BCAA dysmetabolism contributing to insulin resistance and T2DM. Research indicates that BCAA levels are higher in individuals with insulin resistance and T2DM, and that BCAA dysmetabolism may be a key factor in the development of these conditions. However, the exact mechanisms and the role of BCAA supplementation in metabolic health are still under investigation. Overall, BCAAs are more likely to be markers of impaired insulin action rather than direct causes of metabolic disease.Branched-chain amino acids (BCAAs) are essential nutrients that influence metabolic processes and are linked to insulin resistance and type 2 diabetes (T2DM). While BCAA supplementation is often associated with benefits for weight regulation, muscle protein synthesis, and glucose homeostasis, elevated BCAA levels are associated with metabolic dysfunction, insulin resistance, and T2DM. The mechanisms linking BCAA levels to these conditions involve mTORC1 activation, which disrupts insulin signaling, and BCAA dysmetabolism, which leads to mitochondrial dysfunction and β-cell apoptosis. BCAA dysmetabolism is characterized by the accumulation of toxic metabolites, not BCAAs themselves, which contribute to metabolic syndrome and T2DM. Studies suggest that BCAA levels are influenced by factors such as protein degradation, mitochondrial function, and gene expression. Genes like BCKDHA, PPM1K, IVD, and KLF15 are associated with obesity and T2DM. BCAA metabolism is affected in obesity and T2DM, with altered enzyme activity and increased BCAA-related acylcarnitines. The role of BCAA metabolism in these conditions remains complex, with both mTORC1 activation and BCAA dysmetabolism contributing to insulin resistance and T2DM. Research indicates that BCAA levels are higher in individuals with insulin resistance and T2DM, and that BCAA dysmetabolism may be a key factor in the development of these conditions. However, the exact mechanisms and the role of BCAA supplementation in metabolic health are still under investigation. Overall, BCAAs are more likely to be markers of impaired insulin action rather than direct causes of metabolic disease.