People in some developed countries in the Mediterranean region develop heart disease and diabetes less often than do people in other countries. This observation has led some scientists to suggest that a Mediterranean diet might prevent heart disease and diabetes. Compared with the standard U.S. diet, the Mediterranean diet includes larger amounts of nuts, whole grains, fruits, and vegetables. It also includes fewer carbohydrates and larger amounts of “healthy” oil and fat, such as olive oil. The diet has been shown to improve risk factors for heart disease and diabetes in people at risk for those diseases. However, its effects in people who already have the diseases have not been studied, and few direct comparisons of Mediterranean and other diets are available.