Which macronutrient is most energy-dense, providing 9 calories per gram?

Fats are the most energy-dense macronutrient, providing 9 calories per gram. This high caloric content is due to their chemical structure, which contains long chains of carbon and hydrogen that release a significant amount of energy when metabolized. In contrast, carbohydrates and proteins provide about 4 calories per gram each. Vitamins, while essential for various metabolic processes, do not provide calories as they are not a source of energy. This energy density of fats makes them an important source of energy in the diet, especially during periods of energy deficit, and highlights their role in supporting various bodily functions, including hormone production and cell structure.