Which macronutrient provides the most energy per gram?

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

Answer: (C)

The energy density of macronutrients shows that fats provide the most energy per gram. Fats yield about 9 kilocalories per gram, because their molecules are rich in carbon–hydrogen bonds that release a lot of energy when oxidized in the body. In contrast, carbohydrates and proteins each yield about 4 kilocalories per gram, since their structures are more oxidized and contain more oxygen, yielding less energy per gram. Alcohol provides roughly 7 kilocalories per gram, but it isn’t a macronutrient; it’s an energy source, not one of the body’s essential macronutrients. So, fats have the highest energy per gram among macronutrients.