June 21, 2021 -- A new study published in Nutrients investigated the effect of increased dietary potassium from a whole food source--baked/boiled potatoes and baked French fries--or a potassium supplement on blood pressure and other cardiovascular disease risk factors compared to a 'typical American' control diet (lower potassium intake) among 30 pre-hypertensive to hypertensive men and women. Results showed that including baked/boiled potato consumption as part of a typical American diet had the greatest benefit on reducing sodium retention, even more than the supplement, and resulted in a greater systolic blood pressure reduction compared to the control diet. Further, despite commonly held misbeliefs about French fries and their role in heart-healthy lifestyles, the authors observed that a 330-calorie serving of baked French fries, when eaten as part of a typical American diet, had no adverse effect on blood pressure or blood vessel function.
"While significant emphasis is often placed on reducing dietary sodium intakes to better control for blood pressure and cardiovascular disease risk, that's only half of the story," says Connie Weaver, PhD, the primary investigator. "Potassium plays just as an important role, and perhaps the ratio of potassium to sodium is most important in the context of the entire food matrix, as the potato meal resulted in a greater reduction of sodium retention than the potassium supplement alone."
Evidence on the effect of increased dietary potassium on blood pressure from clinical trials is extremely limited, and this is one of the first known controlled feeding interventions investigating dietary potassium as the primary variable of interest.
"It's important to establish clinical trials that follow observational research to establish a causal link between diet and health," notes Weaver. "For example, in this clinical study baked French fries had a null effect on blood pressure, which counters observational findings, at least in the short term, and helps to prioritize the importance of focusing on a total diet approach for maintaining health versus one that overemphasizes avoidance of any single food or food group."
Potatoes comprise roughly 20 percent of the vegetable intake in the American diet and help fill several nutrient gaps, including dietary fiber and potassium.1 Eating just one medium potato meets approximately 10 percent of an adult's daily potassium needs. According to the 2020-2025 Dietary Guidelines for Americans, potassium is an essential nutrient of concern, indicating most Americans aren't consuming enough. The mineral has been linked to improvements in cardiovascular and other metabolic health outcomes - including decreased blood pressure in those with hypertension. Overall, potatoes and French fries represent about 7 percent and 3 percent of potassium intake, respectively, in the United States.1
"Considering Americans fall significantly short in meeting daily potassium intakes, these findings show the importance of promoting, not restricting, whole food good-to-excellent sources of potassium in Americans' diets, like potatoes," Weaver said.
A Closer Look at the Study Methodology, Strengths and Limitations
Participants were randomly assigned to one of four 16-day dietary potassium interventions:
- Control diet including 2300 mg potassium/day (reflective of typical intake, considered to be 'low potassium')
- Control diet + 1000 mg of potassium from potatoes (baked, boiled, or pan-heated with no additional fat)
- Control diet + 1000 mg from baked French fries
- Control diet + 1000 mg from a potassium-gluconate supplement
Each diet was tailored to participants' specific caloric needs while all other nutrients were kept constant. Blood pressure was measured across multiple visits of each phase, and participants also collected daily urine/stool samples to assess potassium and sodium excretion and retention.
The strengths of the study include a highly controlled diet, cross-over design, and excellent compliance. However, the researchers note a few limitations as well, including the study's relatively small sample size, poor retention in study participation and relatively short study duration.
"All clinical studies are faced with limitations; however, despite those found in this study, the rigor of the study design is strong and unlike any other studies that have investigated the effect of a whole food - and potassium - on high blood pressure," Weaver notes. "Through our carefully controlled balance study, we could determine the mechanism by which potatoes reduced blood pressure. Overall, we concluded that boiled or baked potatoes can help reduce systolic blood pressure - and baked French fries have no adverse effects on blood pressure and can be included as part of an overall healthy diet."
The research manuscript, "Short-term randomized controlled trial of increased dietary potassium from potato or potassium gluconate: effect on blood pressure, microcirculation, and potassium and sodium retention in pre-hypertensive-to-hypertensive adults," is published in Nutrients (doi: https://doi.org/10.3390/nu13051610). Authors include Michael Stone, Berdine Martin and Connie Weaver of Purdue University. Funding was provided by the Alliance for Potato Research and Education.