Fats provide the highest energy per gram, yielding approximately 9 kcal/g, which is more than double the energy supplied by proteins and carbohydrates (both ~4 kcal/g). This high energy density makes fats essential for meeting the body's long-term energy requirements and supporting vital functions like cell membrane integrity and hormone synthesis. Unlike vitamins, fats are macronutrients that directly supply energy, crucial for surgical patients who need adequate caloric intake for healing and recovery. Understanding this helps guide nutritional support strategies in clinical settings.

Reference: Guyton and Hall Textbook of Medical Physiology, John E. Hall, 13th Edition.