The present invention addresses the problem of providing a brain function improving agent and a prophylactic or therapeutic agent for cognitive dysfunction, each of which does not induce diarrhea and/or nausea, has a form that is easy to ingest, enables the production of a ketone compound in a human body, is novel and safe, and has little adverse side effects. The present invention provides a brain function improving agent and a prophylactic or therapeutic agent for cognitive dysfunction, each of which comprises a protein, a medium-chain fatty acid triglyceride that serves as a lipid, and a carbohydrate, wherein the protein, the medium-chain fatty acid triglyceride that serves as a lipid and the carbohydrate are contained in amounts of 5 to 50 parts by weight, 5 to 80 parts by weight and 1 to 50 parts by weight, respectively, relative to 100 parts by weight of each of the agents.
