The potato’s rep as a fattening food is getting a much-deserved revision. In a recent report in the American Chemical Society’s Journal of Agricultural and Food Chemistry, scientists note that two small servings of purple potatoes a day reduce blood pressure by about 4 percent—nearly as much as oatmeal—without causing weight gain. The researchers say that decrease may potentially reduce the risk of some forms of heart disease.

In the study, 18 volunteers that were overweight or obese with high blood pressure ate six to eight golf ball-sized purple majesty potatoes, with skins, twice a day for a month. The researchers used purple potatoes because the pigment in darker fruits and vegetables is especially rich in beneficial phytochemicals. They monitored participants’ blood pressure, both systolic (the first number in a blood pressure reading, such as 120/80) and diastolic, and found that the average diastolic pressure dropped by 4.3 percent, while the systolic pressure decreased by 3.5 percent. None of the volunteers gained weight.

Although they aren’t yet certain, the researchers believe that red- and white-skinned potatoes may offer similar benefits. Pass on the butter or sour cream, though, and don’t even consider French fries—the study’s potatoes were cooked without oil.