High-grade gliomas represent the most prevalent primary malignant brain tumors in the adult population. Despite extensive efforts dedicated to advance in therapeutic modalities, treatment options remain very limited in this field, leading to a worse prognosis for affected patients. Moreover, a considerable number of cases exhibit refractory disease following the initial management. Ketogenic Metabolic Therapy (KMT) has emerged as a promising adjunctive approach for recurrent high-grade gliomas, offering them a synergistic effect enhancement of the effectiveness of conventional therapies against this type of cancer. The underlying hypothesis relies on the use of high-fat, low-carbohydrate diet, with adequate protein content can potentially induce metabolic reprogramming in cancer cells. Currently, the use of KMT is on the rise and has shown positive effects on the control of selected neurological symptoms and improvements in patient’s quality of life. This is a descriptive observational multicenter study (case series) that includes patients with recurrent high-grade gliomas who underwent Ketogenic Metabolic Therapy (KMT) and were supplemented with a liquid ketogenic formula (in a 3:1 ratio) as a complementary treatment to the ongoing medical regimen for recurrence. The results show a positive impact on seizure control, as well as significant improvements in cognition, memory and functionality, as reported by patients and/or their families (caregivers). Regarding the disease status, assessed by the RANO criteria, the 12-month follow-up evaluation indicated stable disease in 55% and a partial response in 20% of cases. Although the results of this work are promising, more conclusive clinical data are still needed to support the use of KMT in the treatment of high-grade gliomas.