Proteins are vital for muscle repair, enzyme function, and hormone production, and like carbohydrates, they also supply 4 calories per gram. However, they are a macronutrient, not the unit used to measure energy. The correct term for that measurement is calories. Protein contributes to your daily energy intake, especially when carbohydrates and fats are insufficient, but it is not typically the body’s preferred energy source. Proteins are more often used for building and maintaining tissue. If you were asked about a nutrient that contributes energy, protein could be a valid part of the answer. But when asked what quantifies the energy value of food, the right word is calories.