The present invention relates to a composition comprising a starch or total dietary fiber which improves the cell viability, specifically, the inventive starch and total dietary fiber isolated from the extract of Gramineae plant and the components therefrom improved the cell viability when the cells were incubated under hypoxic condition, or in the presence of beta-amyloid and 6-hydroxydopamine treatment, as well as prevented and treated myocardiac infarction, cerebral infarction and vascular dementia, or alleviated memory loss, all of which were proven using rats as the respective animal models. Therefore, they can be used as therapeutics or health care food for preventing and treating ischemic diseases or degenerative brain diseases.