3-Aminoisobutyric acid, a non-protein amino acid resultant from thymine catabolism, plays a significant role in metabolic activities. At a 5 µM concentration, it triggers browning in primary adipocytes, notably elevating uncoupling protein 1 (UCP-1) and CIDEA expression. Additionally, it boosts PPARα expression in both primary adipocytes and mouse inguinal white adipose tissue (WAT) in vivo, alongside enhancing β-oxidation in hepatocytes. Its plasma levels surge post-exercise in mice, and its administration at 100 mg/kg daily curtails weight gain and body fat without diminishing food consumption or hiking energy output, whilst ameliorating glucose tolerance. Notably, 3-aminoisobutyric acid concentrations are heightened in individuals with β-ureidopropionase deficiency, a genetic flaw impairing pyrimidine degradation, affecting plasma, urine, and cerebrospinal fluid.