The document discusses the four main body systems involved in nutrition: the digestive system, respiratory system, circulatory system, and excretory system. The digestive system transforms food into nutrients using the digestive tract and glands. The respiratory system is responsible for breathing in oxygen and out carbon dioxide. The circulatory system transports nutrients and oxygen to cells using the heart and blood vessels. Finally, the excretory system filters waste from the blood and removes it from the body through excretion.