Eat Right Any kind of nutritional deficiency may lead to more frequent and prolonged illnesses. If you starve yourself, your body will pump out stress hormones. Dropping more than 2 pounds per week is hard on the T cells that detect diseased or foreign cells. Choose fats carefully (omega-3s are good), get enough protein, eat your fruits and vegetables and drink plenty of fluids. "Dehydration lowers resistance," says Lee Berk, Dr.P.H.,M.P.H., an assistant professor of family medicine at the University of California, Irvine, College of Medicine.