A varied and balanced diet plays a crucial role in maintaining a healthy lifestyle. However, for some people suffering from chronic conditions, diet is not just a good practice but a key aspect an integral part of their treatment. A gluten-free diet is currently the only treatment available for people with coeliac disease or gluten-related conditions. A low-protein diet can be a valuable ally in reducing the progression of chronic renal failure. Numerous studies have confirmed the value of the ketogenic diet in cases of fat malabsorption and maldigestion and in the treatment of neurological disorders. One in four adults suffers from metabolic syndrome, in which a correct and balanced diet is an ally in preventing a deterioration in health.