Which body system breaks down food into nutrients that can be used as fuel?

• A. Circulatory
• B. Endocrine
• C. Digestive
• D. Urinary

Answer: (C)

The digestive system is the one that actually breaks down food into nutrients that can be used as fuel. It handles both mechanical and chemical digestion—chewing, stomach churning, and enzymes like amylase, proteases, and lipases that convert carbohydrates, proteins, and fats into simple molecules. These nutrients are then absorbed through the intestinal lining into the bloodstream and delivered to cells, where they’re used to produce energy. Other systems support this process but don’t perform digestion themselves: the circulatory system transports nutrients, the endocrine system regulates digestion with hormones, and the urinary system eliminates waste. So, digestion is the step that turns food into the fuels your body can burn for energy.