The article by Guoyao Wu discusses the multifaceted roles of amino acids (AA) in metabolism, gene expression, and protein phosphorylation. AA are not only essential for protein synthesis but also serve as precursors for hormones and low-molecular-weight nitrogenous substances, playing crucial biological functions. Physiological concentrations of AA and their metabolites are vital for various physiological processes, while elevated levels can lead to neurological disorders, oxidative stress, and cardiovascular disease. The article highlights the importance of maintaining an optimal balance of AA in the diet and circulation for whole-body homeostasis. Additionally, it emphasizes that some AA, known as functional AA, regulate key metabolic pathways essential for maintenance, growth, reproduction, and immunity. Dietary supplementation with these functional AA can benefit health at various life stages and enhance metabolic efficiency, muscle growth, and athletic performance while preventing excess fat deposition. The introduction provides a detailed overview of AA, their chemical properties, and their roles in cell metabolism, with a focus on their catabolic pathways and the importance of the small intestine in AA metabolism.The article by Guoyao Wu discusses the multifaceted roles of amino acids (AA) in metabolism, gene expression, and protein phosphorylation. AA are not only essential for protein synthesis but also serve as precursors for hormones and low-molecular-weight nitrogenous substances, playing crucial biological functions. Physiological concentrations of AA and their metabolites are vital for various physiological processes, while elevated levels can lead to neurological disorders, oxidative stress, and cardiovascular disease. The article highlights the importance of maintaining an optimal balance of AA in the diet and circulation for whole-body homeostasis. Additionally, it emphasizes that some AA, known as functional AA, regulate key metabolic pathways essential for maintenance, growth, reproduction, and immunity. Dietary supplementation with these functional AA can benefit health at various life stages and enhance metabolic efficiency, muscle growth, and athletic performance while preventing excess fat deposition. The introduction provides a detailed overview of AA, their chemical properties, and their roles in cell metabolism, with a focus on their catabolic pathways and the importance of the small intestine in AA metabolism.