The body utilizes fat as a source of energy primarily during low to moderate intensity activities. When exercising, the body first relies on carbohydrates for quick energy and, as activity continues and glycogen stores deplete, it shifts to oxidizing fatty acids. This process is called lipolysis, where stored fats are broken down and converted into usable energy. This capacity to use fat becomes increasingly important during prolonged physical activities and in metabolic adaptations that arise from regular endurance training, enhancing overall endurance and efficiency.