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.

Inclusion Criteria:

1. Diagnosis of hypothalamic-chiasmatic tumour according to the WHO 2021 classification
2. Diagnosis of hypothalamic obesity: after 5 years of age, BMI >97th percentile in the WHO 2007 curves
3. Males and females aged between 7 and 30 years
4. Performance status: Lansky score > 40 for patients aged < 18 years and Karnofsky score > 40 for patients aged between 18 and 30 years
5. Signature of informed consent to participate in the study
6. Signature of consent by the minor patient to participate in the study (7-13 years and 14-17 years).

Exclusion Criteria:

1. Deficiencies of:

• Primary carnitine
• Carnitine palmitoyltransferase 2 (CPT 2)
• Carnitine acylcarnitine translocase (CACT)
• Beta-oxidation
• Medium-chain acyl-CoA dehydrogenase (MCAD)
• long-chain acyl-CoA dehydrogenase (LCAD)
• short-chain acyl-CoA dehydrogenase (SCAD)
• porphyria
• pyruvate carboxylase
• long-chain 3-hydroxyacyl-CoA dehydrogenase.