Which statement is true about energy yield per gram for macronutrients?

• A. Carbohydrates provide about 4 kcal/g
• B. Proteins provide about 4 kcal/g
• C. Alcohol provides about 7 kcal/g
• D. Fats provide about 9 kcal/g

Answer: (D)

Fats carry the most energy per gram among the macronutrients. Their long hydrocarbon chains are highly energy-dense, and when oxidized in metabolism they release a large amount of energy, about 9 kilocalories per gram. In contrast, carbohydrates and proteins yield roughly 4 kilocalories per gram because their structures release less energy per gram when broken down. Alcohol provides about 7 kilocalories per gram, but it isn’t a macronutrient in the same sense and is metabolized differently, so it isn’t the basis for the energy-yield standard for macronutrients. Therefore, the true statement is that fats provide about 9 kcal per gram.