Nutrition is far more important to the prevention of stroke than most physicians realize. Key issues include a Mediterranean diet, the interaction of the intestinal microbiome, impaired renal function and diet, missed metabolic B12 deficiency, and the lowering of homocysteine with B vitamins to prevent stroke. The Cretan Mediterranean diet is high in olive oil, whole grains, fruits, vegetables, and legumes, and is close to a vegetarian diet. Compared with a low-fat diet, it reduced stroke by over 40%, and is clearly the best diet for diabetes. Metabolic B12 deficiency is very common (˜ 30% of stroke patients age > 70 years) and frequently missed because it is not excluded by a total serum B12 level in the reference range. B vitamins to lower homocysteine do prevent stroke, but their benefit was obscured in early studies because of harm from cyanide in cyanocobalamin among participants with renal impairment. Methylcobalamin should be used instead of cyanocobalamin.