Abstract
While free amino acids (FAAs) are often regarded as simple building blocks for proteins, various studies show they have more complex roles in the body. This review expands on the FAA's functions, emphasizing their influence on diverse biological processes. It covers their significance in metabolism, energy production, and the synthesis of neurotransmitters, hormones, and antioxidants. FAAs also serve as signaling molecules that regulate critical pathways related to cell growth, autophagy, and metabolic control. The review highlights their impact on the immune system and their essential roles in gut health, nutrient sensing, and metabolic communication. Drawing on recent findings, we emphasize the importance of measuring FAA levels in biological samples and suggest that their supplementation could be beneficial in clinical nutrition, treating metabolic or immune disorders, and preventing sarcopenia. Overall, FAAs are presented as key signaling agents and biomarkers, with potential for targeting their levels to improve health and treat diseases.