How many calories are in one gram of protein?

How many calories are in one gram of protein?

• A. 4
• B. 9
• C. 7
• D. 5

Answer: (A)

Protein yields about four kilocalories per gram. This figure comes from the general Atwater factors used to estimate energy in foods. When amino acids are oxidized for energy, the usable energy released is about four kilocalories per gram, though not every bit of energy is captured because nitrogen is excreted; so it’s treated as an approximate value. This energy density is the standard used on nutrition labels and in planning diets. By comparison, other macronutrients differ in energy per gram: fat provides more energy per gram than protein, carbohydrates provide roughly the same energy as protein, and alcohol provides less than fat but more than protein.

Protein yields about four kilocalories per gram. This figure comes from the general Atwater factors used to estimate energy in foods. When amino acids are oxidized for energy, the usable energy released is about four kilocalories per gram, though not every bit of energy is captured because nitrogen is excreted; so it’s treated as an approximate value. This energy density is the standard used on nutrition labels and in planning diets. By comparison, other macronutrients differ in energy per gram: fat provides more energy per gram than protein, carbohydrates provide roughly the same energy as protein, and alcohol provides less than fat but more than protein.