During low-intensity exercise, the body primarily uses fat as an energy source through a process called lipolysis. When engaging in activities like walking or light jogging, the body relies on fat oxidation to generate energy, as it is efficient and can fuel prolonged physical activity. This process allows the body to conserve its limited glycogen stores, which are more readily used during high-intensity efforts. Thus, low-intensity exercise is effective for fat burning and improving metabolic health.