A central metabolic intermediate formed when an acetyl group attaches to coenzyme A, acting as the main entry point for fuel into the body’s energy-producing cycles. Carbohydrates, fats, and proteins all converge on acetyl CoA: glucose is converted to it after glycolysis, fatty acids yield it through beta-oxidation, and excess amino acids can be funneled into it as well. Once formed, it either enters the citric acid cycle to generate cellular energy or, when energy is abundant, serves as the starting material for building fatty acids and cholesterol. This hub position explains why nutrition is fundamentally about managing acetyl CoA flow, whether the goal is burning fat, storing it, or sparing protein. Food scientists invoke it to explain how different macronutrients ultimately share a common metabolic currency.