The immune system protects the body from infection and from the formation of cancer. If you're abnormally tired or catch frequent colds or other infections, your immune system may not be working as effectively as it should. Fruits and vegetables contain many infection-fighting vitamins and antioxidants, including vitamins A, B6, C, and E, as well as the minerals zinc and selenium. If you're feeling under the weather, get a nutrition boost by combining your favorite fruits and vegetables in nutrient-rich juices.