This article discusses the function of the digestive system in nutrient absorption and energy balance. The digestive system is responsible for breaking down food into simple molecules, absorbing nutrients into the bloodstream, and eliminating undigested waste products. Nutrients such as carbohydrates, proteins, fats, vitamins, minerals, and water are essential for energy production, growth, tissue repair, and normal physiological function. The article analyzes the main organs of the digestive system, the processes of mechanical and chemical digestion, the role of enzymes, nutrient absorption in the small intestine, and the relationship between digestion and energy metabolism. The study shows that proper digestive function is essential for maintaining energy balance, supporting metabolism, and preserving overall health.