Metabolism and immunity are closely linked. Both overnutrition and undernutrition have implications for immune function. Starvation and malnutrition can suppress immune function and increase susceptibility to infections. Obesity is associated with a state of aberrant immune activity and increasing risk for associated inflammatory diseases, including atherosclerosis, diabetes, airway inflammation, and fatty liver disease. Thus, optimal nutritional and metabolic homeostasis is an important part of appropriate immune function and good health.