A chronic disease is a long-term health condition that is generally manageable but not curable, such as type 2 diabetes, coronary heart disease, asthma, or arthritis. These conditions develop over years, influenced by genetics, environment, and lifestyle, and are the leading causes of death and disability worldwide. Nutrition plays a dual role: dietary patterns high in vegetables, whole grains, and unsaturated fats lower the risk of developing chronic diseases, while medical nutrition therapy helps manage them once diagnosed, controlling blood sugar, blood pressure, and weight. Prevention through healthy habits remains far more effective than treatment after onset.