The effect of daily potato consumption on potassium status and continual blood pressure: a randomised controlled trial

Hypertension affects around 30% of UK adults and accounts for approximately 54% of strokes and 47% of heart disease globally (1) . Sodium (Na+) reduction remains the primary diet-focused therapy for lowering blood pressure (BP), however, the decline in intake has plateaued over the last decade (2) . Increasing dietary potassium (K+), a shortfall nutrient in the UK, may offer an alternative means of reducing Na+ retention via the “K+ switch”, leading to clinically meaningful reductions in both systolic and diastolic blood pressure (3) . Potatoes, the richest source of dietary K+ per portion, may offer a practical means to increase intake. The STARCHy study, a single-blinded randomised controlled trial (NCT05994313), investigated whether replacing refined starches with a daily portion of potatoes could improve K+ status and BP in UK healthy adults aged 40–80 years. Dietary intake was assessed using 4-day food diaries and analysed in Nutritics (Dublin, Ireland). Twenty-four-hour urinary K+ was analysed using flame photometry, and serum K+ by ion-selective electrode (Siemens Advia 1800 clinical chemistry analyser). BP was recorded using validated optical bracelets (Hilo SA, Neuchâtel, Switzerland), worn continuously throughout the intervention. Linear mixed-effects models assessed treatment effects for BP, urinary K+, and dietary K+, with participant ID as a random effect. Ordinary Least Squares regression was used for serum K+. All models were adjusted for baseline values, age, sex and BMI and analysed in Stata 18 (StataCorp. 2024). Seventy-one participants (83% female; mean ± SD age 55 ± 9; BMI 25 ± 4 Kg/m2) were randomised to consume either 230g/day of potatoes (providing approximately 1000 mg K+) or an isocaloric refined starch control (rice, pasta, couscous or bread); 69 participants completed. Baseline systolic and diastolic BP were 117 ± 16 and 80 ± 9, respectively. Dietary K+ intake and serum K+ concentrations were higher in the potato group than the control (adjusted mean differences: 589 mg; 95% CI: 320, 858, P < 0.001, and 0.11mmol; 95% CI: 0.01, 0.21 P = 0.025, respectively). There was a trend towards greater urinary K+ excretion (316 mg; 95% CI: –7.8, 641, P = 0.056) and a lower urinary Na:K ratio (-0.20 95% CI: -0.40, 0.01 P = 0.06), which when restricting analyses to complete urine collections demonstrated significant effects in urinary K+ excretion (698mg; 95% CI: 74, 1321, P = 0.028). No significant between-group differences in daytime, nighttime or 24-hour SBP or DBP were observed (all P > 0.05). Increasing potato intake can improve K+ status, offering a strategy to help bridge the UK’s dietary shortfall, however, this did not lower blood pressure. The modest K+ increase, or the inclusion of most normotensive participants, may explain the lack of effect. Future studies should focus on hypertensive populations.