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INTRODUCTION: Ketogenic diet (KD) results in mild to moderate ketosis, which in turn can significantly change the metabolic balance in the brain. The effects of KD are broadly studied in search of potential clinical uses, such as reducing seizure severity in epilepsy, or providing adjunctive therapy for cancer, Alzheimer’s or Parkinson’s disease. The exact mechanism of those putative neuroprotective effects of KD is, however, still poorly understood. AIM(S): Here, we have checked if prolonged ketogenic diet changed beta hydroxy butyrate(BHB) and epididymal fat levels. The crucial thing was to determine how the ketogenic diet affects brain volume and anatomy. METHOD(S): Male Wistar rats were assigned into two experimental groups: one was given KD for 4 months (n=10), the other (n=11) was fed normal laboratory chow (N). After 4 months, rats were sacrificed. Blood samples were collected and BHB levels measured with ELISA. T2-weighed ex vivo images of extracted brains, taken with a 9.4 T magnetic resonance scanner were obtained at the Institute of Nuclear Physics, at XY resolution of 0.025 mm and voxel depth of 0.25 mm. Using a computer-assisted Cavalieri method, the volumes of the entire brain, hippocampus and brainstem structures (midbrain, pons) were estimated. Volumes were compared between groups to show differentially affected regions. Student’s t‑tests was used for statystical analysis. RESULTS: We have observed increased epididymal fat and elevated BHB levels in KD in comparison to the N group (p<0,000001). Additionally we have found a significant reduction in overall pontine volume in the KD group after the 4-month feeding period. CONCLUSIONS: Our results indicate that the prolonged ketogenic feeding was successful in inducing metabolic changes in KD animals. Observed differences in pontine volume in rats fed a ketogenic diet may lead to modification of feeding behavior. These imapairments in food-intake process may be strictly involved with parabrachial structures which are engaged in regulating appetitive behavior. FINANCIAL SUPPORT: Supported by NCS GRANT: UMO-2015/17/B/NZ7/02953.