The food group primarily responsible for energy production is carbohydrates. Carbohydrates are converted into glucose, which serves as the primary energy source for the body's cells. During physical activity, especially high-intensity workouts, the body relies heavily on glucose for immediate energy needs. Fats also provide energy but are utilized more during prolonged, lower-intensity activities. In summary, while both carbohydrates and fats serve this role, carbohydrates are the most efficient energy source, particularly for engaging in rigorous physical activities.