To supply 900 kilocalories purely from macronutrients, how many grams of protein would be required and how does this compare to the grams of fat required to supply the same energy (fat = 9 kcal/g)? Show the calculations and interpret which macronutrient is more energy-dense.

• A. 100 g of protein and 225 g of fat; because protein stores concentrate energy more effectively in the body than fat
• B. 300 g of protein and 50 g of fat; assuming protein yields extra ATP via nitrogen salvage and thus requires more mass but ultimately fewer net calories
• C. 225 g of protein and 100 g of fat; fat is more energy-dense requiring fewer grams for equal energy
• D. 150 g of protein and 150 g of fat; because both macronutrients are metabolized into similar ATP yields per gram after accounting for deamination losses

Answer: (C)