Hypothalamic-chiasmatic tumours account for 5-10% of CNS tumours in children and can compromise hypothalamic function, causing alterations in energy balance and weight gain. In inoperable cases, chemotherapy and radiotherapy are used; the latter, although the gold standard, is associated with significant neurocognitive and endocrine-metabolic side effects, proportional to the hypothalamic damage. The ketogenic diet, used for decades in the treatment of drug-resistant childhood epilepsy, induces the use of ketone bodies as a source of energy for the brain and is effective in controlling seizures. Among the different variants, the modified Atkins diet was chosen in this study to promote better patient adherence. This study aims to evaluate the effectiveness of the ketogenic diet (KD) in treating central obesity secondary to hypothalamic-chiasmatic tumours (gliomas, craniopharyngiomas, germ cell tumours, etc.), which often lead to excessive weight gain. This is refractory to drug therapy and lifestyle changes, such as low-calorie diets and exercise.