This clinical trial is for men and women with high-grade gliomas. Glucose (sugar) is thought to be a contributor to tumor growth. The ketogenic diet (a high fat, low carbohydrate diet) and metformin (a drug approved by the Food and Drug Administration to treat type 2 diabetes) are both known to lower blood glucose levels. 
    
The purpose of the study is to evaluate the tolerability of a ketogenic diet in conjunction with metformin and whether maintaining and the diet with metformin will have any effect on your tumor. Participants will continue on treatment as long as they are responding to therapy and not experiencing unacceptable side effects.