The Centers for Disease Control reports that the diet and lifestyles of over 300,000 people over 8 European countries were studied. Those who ate at least 8 servings of fruits and vegetables a day had a 22% lower risk of dying from heart disease than those who ate 3 servings a day. They estimated that each additional serving of a fruit or vegetable per day was linked to a 4% lower risk of death from cardiovascular disease. One portion is about 80 grams, which would be roughly equivalent to a medium apple, a small carrot or small banana.
Since heart disease is the leading cause of death in the US, accounting for about 25% of all deaths, this is wise advice.