The ketogenic diet, a high-fat, low-carbohydrate dietary approach, is increasingly used as a therapeutic strategy for the treatment of drug-resistant epilepsy and neurodegenerative diseases such as Alzheimer’s and Parkinson’s disease. The primary mechanism of the ketogenic diet is the induction of a state of ketosis, during which the brain begins to use ketone bodies. Not only do ketones replace glucose as a fuel but also exhibit a number of neuroprotective effects, such as reducing oxidative stress, stabilising mitochondrial function, mitigating excitotoxicity, reducing neuroinflammatory signalling pathways, and stimulating autophagy. In drug-resistant epilepsy, the ketogenic diet can significantly reduce seizure frequency, especially in children with metabolic syndromes (glucose transporter type 1 deficiency syndrome, pyruvate dehydrogenase complex deficiency). In Alzheimer’s disease, the ketogenic diet improves cerebral metabolism, reduces β-amyloid deposition, and supports cognitive function, especially in the early stages of the disease. In Parkinson’s disease, a reduction in non-motor symptoms, improvement in mood and mitochondrial function, and potential modulation of the gut microbiota have been observed. However, it should be noted that the ketogenic diet is not without side effects, which include gastrointestinal disorders, hypoglycaemia, lipid abnormalities, kidney stones, micronutrient deficiencies, and possible stunted growth in children. Contraindications, on the other hand, include metabolic diseases, liver and kidney failure, type 1 diabetes, and pregnancy. In conclusion, the ketogenic diet is a promising non-pharmacological therapeutic option in neurology. However, its use requires individual assessment, specialised supervision, and further multicentre studies to confirm long-term efficacy and safety.