People who ate purple potatoes cooked in the microwave twice a day for a month lowered their blood pressure by 3 percent to 4 percent, U.S. researchers say. Joe Vinson of the University of Scranton in Pennsylvania said the blood pressure-lowering effects are likely due to the high concentration of potatoes\' antioxidants -- which protect the body from \"free radicals,\" or molecules that can damage healthy cells. \"Mention \'potato\' and people think \'fattening, high carbohydrates, empty calories.\' In reality, when prepared without frying and served without butter, margarine, or sour cream, one potato has only 110 calories and dozens of healthful phytochemicals and vitamins,\" Vinson said in a statement. \"We hope our research helps to remake the potato\'s popular nutritional image.\" Potatoes contain a variety of potentially beneficial phytochemicals at similar levels as broccoli, spinach and Brussels sprouts, but not if they are deep fried as French fries or potato chips, Vinson said. In the study, 18 overweight and obese people with high blood pressure ate six to eight golf ball size purple potatoes with the skins twice daily or no potatoes, as a part of their normal diet for four weeks. The findings, presented at the national meeting of the American Chemical Society in Denver, showed those who ate purple potatoes lowered their diastolic blood pressure -- the bottom number in a blood pressure reading -- by an average of 4.3 percent and systolic -- the top number -- by 3.5 percent. Vinson said although the study used purple potatoes, red and white potatoes might have similar effects.