Which nutrient yields 9 kcal per gram?

• A. Carbohydrates
• B. Protein
• C. Alcohol
• D. Fat

Answer: (D)

Energy density of macronutrients matters: fats provide the most energy per gram. Fat delivers about 9 kcal per gram, while carbohydrates and proteins each provide about 4 kcal per gram, and ethanol provides about 7 kcal per gram. The reason fat is so energy-dense is its chemical structure—long carbon-hydrogen chains with relatively little oxygen. When these fats are oxidized for energy, the numerous carbon-hydrogen bonds release more energy per unit mass than the bonds found in carbohydrates or proteins. So fat is the nutrient that yields 9 kcal per gram. Carbohydrates and proteins give roughly 4 kcal per gram, and alcohol gives about 7 kcal per gram but is not categorized as a nutrient in the same sense.