This document discusses how malnutrition affects immunity. It defines malnutrition as a lack of proper nutrients that the body needs to function optimally. There are two types: undernutrition from not enough calories/nutrients and overnutrition from too many calories/fat. Malnutrition increases risk of infection due to deficiencies in the immune system, including reduced complement system functions, fewer phagocytes, and decreased antigen presentation. It also decreases hematopoiesis. Overall, malnutrition significantly weakens both innate and adaptive immunity.