Diffuse gliomas are incurable brain cancers. Amongst these, glioblastoma (GB) is the most aggressive primary brain tumor and has a poor prognosis despite the use of multimodal therapy. Therefore, novel therapeutic approaches are urgently needed. Calorie-restricted diets have emerged as putative strategy to augment anti-cancer therapies. We employed UHPLC-high resolution mass spectrometry analyses of plasma lipids and polar metabolites to assess systemic metabolic effects of a 72 h pre-surgery fasting course in IDH-wildtype glioma patients (n = 9 GB and n = 1 diffuse pediatric type high-grade H3/IDH wildtype) who participated in the prospective ERGO3 trial (NCT04461938). Fasting reduced lysophosphatidylcholines (LPC) and lysophosphatidylethanolamines (LPE) and their ether-bound derivatives (LPC-O, LPE-O), and increased free fatty acids and carnitines. Triglyceride (TG) profiles shifted from short-chain TGs (42-48 C-atoms, reduced) to very long chain TGs (58-60 C-atoms, increased) indicating an exploitation of neutral lipid stores. Branched chain amino acids, aminobutyric acid and uric acids were increased, and glucose reduced as expected after fasting. Analyses of individual lipid/metabolite profiles in comparison with the average profile revealed that all subjects adhered to the fasting scheme with interindividual substantial differences in fasting efficacy, apparently independent from BMI, MGMT promoter methylation status or low-dose dexamethasone treatment. LPCs were reduced in all fasted patients. This is to our knowledge the first study that evaluated effects of fasting on systemic lipid/metabolite levels in GB patients. Our results are a prerequisite for advancing fasting interventions as a component of a potential metabolic tumor therapy. A fasting-induced systemic reduction of LPCs may reduce LPC-dependent omega-3 lipid import into the brain and, hence, lipid supply necessary for glioma growth.