Normal brain switches to utilization of ketone bodies only during prolonged starvation. It is not known whether brain tumors can utilize ketone body under in vivo conditions. There are ongoing clinical trials on using ketogenic diet as adjuvant therapy for the treatment of brain tumors. Here, we show that brain tumors (meningioma and GBM) can fully oxidize ketone body and therefore ketogenic diet may not be effective in the treatment of these tumor patients. MCT1 is involved in the transport of BHB into tumor cells and therefore it is feasible to target BHB metabolism using MCT1 inhibitor.