Potatoes may be getting a bum rap, according to a small new study that finds that people who ate potatoes daily saw a drop in blood pressure after a month.
The key is that study participants ate potatoes cooked in the microwave, which preserves the tuber’s nutrients — unlike frying them into French fries or chips — the authors said. “Mention ‘potato’ and people think ‘fattening, high-carbs, empty calories,’” said lead researcher Joe Vinson in a statement. “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.”
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The research involved a tiny sample size — just 18 people. All were hypertensive, and 14 of the participants were already taking blood-pressure lowering medication and most were overweight or obese. Half the participants ate six to eight microwaved purple potatoes (each roughly the size of a golf ball), with the skins on, twice daily. The other half made no change to their daily diets. After a month, the two groups switched regimens.
Researchers found at the end of the study that potato eating was associated with reductions in systolic (the top number) and diastolic (the bottom number) blood pressure readings of 3.5% and 4.3%, respectively. People taking blood pressure medication also saw reductions. And eating potatoes didn’t result in weight gain or a rise in cholesterol level.
The researchers said that purple potatoes in particular have high amounts of antioxidants and other nutrients, especially in the skin.
Of course, the study was small and short-term and included hypertensive people with weight problems, so it’s difficult to extrapolate anything to a wider population. And the findings, which were presented at the National Meeting & Exposition of the American Chemical Society (ACS) this week, are not yet peer-reviewed and must be considered preliminary. It’s also worth noting that the study was funded by the U.S. Department of Agriculture.
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Nevertheless, the report is a good reminder that even the most healthful foods can be turned into junk with the wrong preparation.
Meredith Melnick is a reporter at TIME. Find her on Twitter at @MeredithCM. You can also continue the discussion on TIME’s Facebook page and on Twitter at @TIME.