Step 1: Energy value of nutrients: carbohydrates ≈ 4 kcal per gram, proteins ≈ 4 kcal per gram, fats ≈ 9 kcal per gram. Step 2: Vitamins do not give energy; they regulate body functions. Step 3: Therefore fats give more than twice the energy of carbohydrates or proteins per gram. Step 4: This is why fat is the best way for the body to store energy, but eating too much of it leads to obesity. Answer: Fats.