A 100 g snack contains 20 g fat, 30 g carbohydrate, and 10 g protein. If you replace 10 g fat with 10 g carbohydrate (keeping total weight 100 g), how does the total calorie content change? (Use fat = 9 kcal/g; carb/protein = 4 kcal/g).

• A. Total calories decrease by 150 kcal because fat contributes much more energy per gram in this context
• B. Total calories remain unchanged because mass is conserved even when macronutrients change
• C. Total calories decrease by 50 kcal
• D. Total calories increase by 50 kcal due to higher carbohydrate proportion

Answer: (C)