An energy imbalance can lead to nutritional diseases such as obesity, diabetes, cancer, anorexia. . . The main causes of these nutritional diseases are due to poor diet: energy intake is not in line with needs and physical activity. Poor diet is at the root of nutritional diseases. These diseases are treated by dietary management, which involves dietetics and constitutes a form of dietary therapy. If left untreated or poorly managed, these nutritional diseases can lead to severe complications. This calls for a multidisciplinary approach, with different fields of expertise: general practitioners, dieticians, nutritionists, clinical psychologists, etc.