I do A level Geography and within the topic of Health we do a case study on Obesity as a disease of affluence. Diseases don't have to be infectious, and they can be self-inflicted. Obesity fits the definition for disease because long-term it can have severe effects on the body and can lead to death if untreated. In the same vein, malnutrition doesn't have to mean starving-many obese people suffer from malnutrition.