The document discusses the four main body systems involved in nutrition: the digestive system, respiratory system, circulatory system, and excretory system. The digestive system breaks down food and absorbs nutrients. The respiratory system inhales oxygen and exhales carbon dioxide during breathing. The circulatory system transports nutrients, oxygen, and waste throughout the body via blood and blood vessels. The excretory system filters waste from the blood and removes it from the body through sweat and urine. Together these four systems work to provide cells with nutrients and remove waste.