How many kcal per gram are in proteins?

• A. 9 kcal/g
• B. 7 kcal/g
• C. 0 kcal/g
• D. 4 kcal/g

Answer: (D)

Proteins provide about 4 kcal per gram when metabolized. This value comes from the Atwater factors used to estimate the energy content of foods. While proteins are mainly for tissue building and other biological roles, they can be oxidized for energy, yielding roughly 4 kcal for each gram of protein consumed. The higher numbers belong to fat (about 9 kcal per gram) and alcohol (about 7 kcal per gram), and a zero-energy value would be incorrect because protein catabolism does contribute usable energy, albeit not as efficiently as fat. This 4 kcal/g figure is the standard used in nutrition labeling and dietary planning.