For decades, nutrition science focused primarily on omega-3 and omega-6 fatty acids. New research now suggests that C15:0 (pentadecanoic acid), a naturally occurring odd-chain saturated fatty acid, may represent an overlooked essential nutrient. Early evidence indicates C15:0 may support mitochondrial function, reduce inflammation, stabilize cell membranes, improve insulin sensitivity, and potentially influence longevity pathways involved in healthy aging.