STARchy Staples: a Randomised Controlled Trial on Cardiometabolic Health (STARCHy)

An investigation into habitual potato consumption (mashed, boiled, baked) on sleep quality and chronic glycaemic control, established risk factors for cardiometabolic diseases, versus habitual consumptions of non-nutrient-dense starchy staples (white rice, pasta, and couscous).

Study Overview

• Status: Completed
• Conditions: Cardiometabolic Health
• Intervention / Treatment: Dietary supplement: Habitual potato consumption; Dietary supplement: Habitual non-nutrient-dense staple consumption

Detailed Description

In the last few years, researchers have undergone efforts to conduct well-controlled trials to investigate the cardiometabolic health effect of consuming potatoes as part of a healthy diet. None to our knowledge, however, have investigated the harmful dyad of poor sleep and adverse glycaemic control, 2 interrelated factors which can exacerbate cardiometabolic (CM) health outcomes. The nutrient density of potatoes, namely being the single richest source of potassium per serving, provides a plausible mechanism in which the potatoes may act to improve health markers.

The primary objective of this study is to investigate whether consuming a portion of nutrient-dense potatoes in the evening meal, in place of other refined carbohydrates, can improve sleep quality, and improve nocturnal, and 24-hour, glycaemic control, both risk factors for CM diseases. Secondly, this study aims to investigate the effects of potato consumption on endothelium-dependent vasodilation, which can further interrelate to this web of interactions, and other measures of CM health.

Study design: A randomised, two-parallel arm, in-clinic and remote, 12-week dietary intervention study.

Study population: Healthy male and female 40-80-year-olds, who consume ≤4 fruits and vegetables per day and have sub-optimal sleep quality.

The study aims to recruit a total of 80 participants, allowing for an estimated 15% dropout rate, to reach 80% power at a significance level of 0.025 (based on two outcomes). The allocation ratio is 1:1 intervention to control.

Statistical analysis: Differences between groups (minimized for age, gender, BMI) will be analysed using Linear mixed models for outcomes with 3 timepoints (urinary outcomes, dietary intake data), with change being the dependent factor, subject ID as a random effect, treatment and season as fixed effects, and baseline outcome and BMI as covariates. Variables with 2 timepoints will be assessed with an ANCOVA regression model.

Locations:

Metabolic Research Unit, 4th floor, Franklin Wilkins Building, Waterloo campus, Kings College London, SE1 9NH.

Screening assessment: Participants will be initially assessed for suitability against the inclusion-exclusion criteria via an online questionnaire. The outputs of the questionnaire will be assessed by the study team. Some exclusion criteria will be assessed at the baseline clinic visit before any baseline measures are provided.

Study duration: There will be a 2-week run-in period, followed by a 12-week dietary intervention.

Dietary intervention: The intervention (potato group) will consume at least 230 g of white potatoes (including fresh and frozen baked, boiled, and mashed potato products) in their evening meal, providing ~1000 mg potassium, enough to increase national median intakes up to recommended intakes. The control group will consume isoenergetic amounts of non-nutrient-dense starchy staples (white pasta, white rice, or couscous).

Although participants cannot be blinded to what they're consuming, they will be blinded to whether they are in the control or the intervention group, to reduce the risk of bias.

Participants will be required to source the potatoes and make these meals themselves, however, they will be provided with rotating 4-weekly recipe cards, with instructions on how to prepare meals.

Participants will be required to attend several virtual one-to-ones with the study team, including an introductory call, a virtual run-in induction where they will be run through the study equipment, and 2 in-person clinic visits. Participants will be responsible for applying some study equipment from home, to reduce clinic visits and improve study retention.

Compliance: Compliance will be monitored via several methods. Firstly, 24 h urinary potassium excretion, which is shown to recover 75% of potassium intake, secondly self-reported compliance will be measured through evening meal checklists. We also plan to use dietary recalls at weeks 2, 4, and 8 to reinforce dietary advice, and to make adaptations to rotating menus based on individual needs, if participants are struggling with adherence. Detailed dietary intake will be assessed through 4-day food diaries at weeks 0, 6, and 12- this data will be used for analysis.

Flow-mediated dilation: A Doppler ultrasound will be utilised to capture continuous ultrasound videos to measure flow-mediated dilation. These will be analysed with automated software provided by Maastricht University.

Anthropometry: Weight, height, waist and hip circumference, blood pressure, and body fat will be taken using standard procedures, in duplicates by a trained researcher at baseline and endline clinic visits.

Blood samples: Fasting blood samples will be collected from a superficial antecubital vein via venepuncture before and after the dietary intervention, by a trained researcher.

Participants will be asked to record and monitor the following information:

Self-reported compliance with dietary intervention, weekly weight (data diaries), and habitual dietary intake (4-day diet diaries).

• Study Type: Interventional
• Enrollment (Actual): 71
• Phase: Not Applicable

Contacts and Locations

Study Locations

• United Kingdom
  • London
    • Lambeth, London, United Kingdom, SE1 9NH
      • Department of Nutritional Sciences, Franklin Wilkins Building, Waterloo campus.

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: Adult; Older Adult
• Accepts Healthy Volunteers: Yes

Description

Inclusion Criteria:

• Self-reported healthy adults
• Aged 40-80 years old
• Intake of ≤4 portions of fruits and vegetables (excluding potatoes) per day
• Low sleep quality index of >5 (Pittsburgh sleep quality index).

Exclusion Criteria:

• Shift workers and those with multiple jobs or carers who are required to wake through the night
• Unwilling to refrain from dietary supplements
• Unwilling to follow protocol and/or give informed consent
• Diagnosed with Cardiovascular Disease (CVD), Type 2 Diabetes, Celiac disease, Insomnia, Sleep apnoea
• Presence of gastrointestinal disorder
• Users of drugs that are likely to alter gastrointestinal motility or nutrient absorption
• History of substance abuse or alcoholism
• Currently pregnant, planning pregnancy, breastfeeding, or having had a baby 12 months prior
• Weight change of >3kg in the preceding 2 months
• BMI <18.5kg/m2 or > 35kg/m2,
• Current smokers, or individuals who quit smoking in the last 6-months
• Frequently consume wholemeal products (1-2 times per day, in the short screening FFQ)
• Never consumed refined starchy staples, such as white pasta or rice (rarely or never, in the short screening FFQ)
• High potato consumption (4-6 times per week, in the short screening FFQ)
• High risk of obstructive sleep apnoea (answer yes to >3 questions, in STOP-Bang questionnaire)
• Vegetarian, Vegan, or pescatarian dietary preferences.
• Diagnosed with mental health disorders, and/or on medicine for their mental health (antipsychotics, antidepressants, beta-blockers)
• Chronic user of antihistamines
• Fasting glucose >7mmol/l (finger prick test at baseline clinic)
• Is taking weight loss, or glucose regulating medications.
• Has been unstable on blood pressure lowering medications for at least 3-months prior to enrollment.

Study Plan

How is the study designed?

Design Details

• Primary Purpose: Basic Science
• Allocation: Randomized
• Interventional Model: Parallel Assignment
• Masking: Single

Number of Arms

2

Arms and Interventions

Participant Group / Arm	Intervention / Treatment
Active Comparator: Habitual non-nutrient-dense staple consumption; Isocaloric amounts of non-nutrient-dense starchy staples, such as white rice, white pasta, and white couscous, will be consumed in the evening meal for 12 weeks.	Dietary supplement: Habitual non-nutrient-dense staple consumption; White rice, white pasta or white couscous are to be consumed in the evening meal, every evening for 12-weeks.
Experimental: Habitual potato consumption; At least 230g of white potatoes, including fresh and frozen, baked, boiled, and mashed potatoes, will be consumed in the evening meal, in replacement of non-nutrient-dense starchy staples, for 12 weeks.	Dietary supplement: Habitual potato consumption; Potatoes are to be consumed in the evening meal, every evening for 12-weeks.

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Change in 7-day sleep efficiency	Differences in % sleep efficiency at endline vs baseline. Sleep efficiency % is described as the total time spent asleep/ total time spent in bed x 100.	Pre- and post-intervention: 12 weeks
Change in 12-day nocturnal mean glucose	Differences in mean nocturnal glucose, measured using a Freestyle Libre 3 continuous glucose monitor.	Pre- and post-intervention: 12 weeks

Secondary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Change in blood pressure	Diastolic and systolic blood pressure, measured by oscillometry.	Pre- and post-intervention: 12 weeks
Change in plasma lipids	Including: total lipids, HDL and LDL-cholesterol, and Triacylglycerols.	Pre- and post-intervention: 12 weeks
Change in fasting plasma glucose	Fasting plasma glucose concentration	Pre- and post-intervention: 12 weeks
Change in fasting insulin	Fasting insulin concentration	Pre- and post-intervention: 12 weeks
Change in fasting HbA1C	Fasting HbA1C concentration	Pre- and post-intervention: 12 weeks
Change in sleep duration, in minutes	Sleep duration (minutes)	Pre- and post-intervention: 12 weeks
Change in sleep duration, in %	Sleep duration (%)	Pre- and post-intervention: 12 weeks
Change in sleep latency	Sleep latency is defined as the time it takes to fall asleep from the time intended to fall asleep.	Pre- and post-intervention: 12 weeks
Change in body fat %	Body fat % measured using TANITA bioelectrical impedance scales	Pre- and post-intervention: 12 weeks
Change in waist circumference (cm)	Waist circumference (cm)	Pre- and post-intervention: 12 weeks
Change in BMI kg/m2	BMI kg/m2, measured using a stadiometer and TANITA scales	Pre- and post-intervention: 12 weeks
Change in mean nocturnal AUC	Difference in 12-day mean nocturnal Area Under the Curve (AUC).	Pre- and post-intervention: 12 weeks
Difference in nocturnal TIR	Difference in 12-day nocturnal Time In Range for non-diabetic populations (TIR nd).	Pre- and post-intervention: 12 weeks
Change in the nocturnal CV%	Difference in 12-day nocturnal coefficient of variation (CV%)	Pre- and post-intervention: 12 weeks
Change in nocturnal MAGE	Difference in 12-day nocturnal Mean Amplitude of Glycemic Excursions (MAGE).	Pre- and post-intervention: 12 weeks
Change in nocturnal MODD	Difference in 12-day nocturnal Mean of Daily Differences (MODD).	Pre- and post-intervention: 12 weeks
Change in mean daytime glycaemic control	Differences in 12-day mean daytime glucose.	Pre- and post-intervention: 12 weeks
Difference in daytime TIR	Difference in 12-day daytime Time In Range for non-diabetic populations (TIR nd).	Pre- and post-intervention: 12 weeks
Change in the daytime CV%	Difference in 12-day daytime coefficient of variation (CV%)	Pre- and post-intervention: 12 weeks
Change in daytime MAGE	Difference in 12-day daytime Mean Amplitude of Glycemic Excursions (MAGE).	Pre- and post-intervention: 12 weeks
Change in daytime MODD	Difference in 12-day daytime Mean of Daily Differences (MODD).	Pre- and post-intervention: 12 weeks
Change in mean 24-hour glycaemic control	Differences in 12-day mean 24-hour glucose.	Pre- and post-intervention: 12 weeks
Difference in 24-hour TIR	Difference in 12-day 24-hour Time In Range for non-diabetic populations (TIR nd).	Pre- and post-intervention: 12 weeks
Change in the 24-hour CV%	Difference in 12-day 24-hour coefficient of variation (CV%)	Pre- and post-intervention: 12 weeks
Change in 24-hour MAGE	Difference in 12-day 24-hour Mean Amplitude of Glycemic Excursions (MAGE).	Pre- and post-intervention: 12 weeks
Change in 24-hour MODD	Difference in 12-day 24-hour Mean of Daily Differences (MODD).	Pre- and post-intervention: 12 weeks
Change in heart rate variability during mental stress	A combination of time domain, frequency domain and non-linear methods (NN intervals, heart rate, rMSSD, pNN50, SDNN, TINN, SDANN, SD1/SD2, High Frequency, Low Frequency, Very Low Frequency, Ultra Low Frequency HF:LF, total power), will be compared from pre- to post-mental stress.	Pre- and post-intervention: 12 weeks
Change in 24-hour heart rate variability	A combination of time domain, frequency domain and non-linear methods (NN intervals, heart rate, rMSSD, pNN50, SDNN, TINN, SDANN, SD1/SD2, High Frequency, Low Frequency, Very Low Frequency, Ultra Low Frequency HF:LF, total power).	Pre- and post-intervention: 12 weeks
Change in Endothelial function	Mean differences in flow-mediated dilation (%)	Pre- and post-intervention: 12 weeks
Nocturnal continuous blood pressure	Measured with an Aktiia Photoplethysmography watch.	Whole 12 week period.
Daytime continuous blood pressure	Measured with an Aktiia Photoplethysmography watch.	Whole 12 week period.
Change in serum potassium	Serum potassium mmol/L	Pre- and post-intervention: 12 weeks
Calystegine potato biomarker	Calystegine will be analysed as an exploratory biomarker of potato consumption (a polyhydroxylated nortropane alkaloid), by Triple Quadrupole mass spectrometry (MS/MS).	Pre- and post-intervention: 12 weeks

Other Outcome Measures

Outcome Measure	Measure Description	Time Frame
Change in meal satiety	Mean difference in area under the satiety curve (exploratory)	Total of 15 satiety scales: 1 pre- and 4 postprandial scales (-1, 1, 2, 3 hours after), in 3 in food diaries (week 0, week 6 and week 12).

Collaborators and Investigators

• Sponsor: King's College London
• Collaborators: Maastricht University; Alliance for Potato Research and Education
• Investigators: Principal Investigator: Wendy Hall, PhD, King's College London

Publications and helpful links

General Publications

• Johnston EA, Petersen KS, Kris-Etherton PM. Daily intake of non-fried potato does not affect markers of glycaemia and is associated with better diet quality compared with refined grains: a randomised, crossover study in healthy adults. Br J Nutr. 2020 May 14;123(9):1032-1042. doi: 10.1017/S0007114520000252. Epub 2020 Jan 22.
• Robertson TM, Alzaabi AZ, Robertson MD, Fielding BA. Starchy Carbohydrates in a Healthy Diet: The Role of the Humble Potato. Nutrients. 2018 Nov 14;10(11):1764. doi: 10.3390/nu10111764.
• McGill CR, Kurilich AC, Davignon J. The role of potatoes and potato components in cardiometabolic health: a review. Ann Med. 2013 Nov;45(7):467-73. doi: 10.3109/07853890.2013.813633. Epub 2013 Jul 15.
• Stone MS, Martin BR, Weaver CM. Short-Term RCT 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. Nutrients. 2021 May 11;13(5):1610. doi: 10.3390/nu13051610.
• Macdonald-Clarke CJ, Martin BR, McCabe LD, McCabe GP, Lachcik PJ, Wastney M, Weaver CM. Bioavailability of potassium from potatoes and potassium gluconate: a randomized dose response trial. Am J Clin Nutr. 2016 Aug;104(2):346-53. doi: 10.3945/ajcn.115.127225. Epub 2016 Jul 13.
• D'Elia L, Masulli M, Cappuccio FP, Zarrella AF, Strazzullo P, Galletti F. Dietary Potassium Intake and Risk of Diabetes: A Systematic Review and Meta-Analysis of Prospective Studies. Nutrients. 2022 Nov 12;14(22):4785. doi: 10.3390/nu14224785.

Study record dates

Study Major Dates

• Study Start (Actual): September 9, 2023
• Primary Completion (Actual): May 1, 2025
• Study Completion (Actual): May 1, 2025

Study Registration Dates

• First Submitted: August 1, 2023
• First Submitted That Met QC Criteria: August 15, 2023
• First Posted (Actual): August 16, 2023

Study Record Updates

• Last Update Posted (Estimated): September 16, 2025
• Last Update Submitted That Met QC Criteria: September 10, 2025
• Last Verified: August 1, 2025

More Information

Terms related to this study

• Keywords: Glycemic control; Flow mediated dilation; Sleep efficiency
• Other Study ID Numbers: RCT-DNS-SS-2023

Plan for Individual participant data (IPD)

• Plan to Share Individual Participant Data (IPD)?: YES

IPD Plan Description

The study protocol, Statistical Analysis Plan, and Informed Consent have been uploaded on 01/09/2025, before statistical analysis commenced.

De-identified data will be shared upon reasonable request and in collaboration with the study investigators, beginning 12 months after publication of the main trial results.

• IPD Sharing Time Frame: Protocol, SAP and ICF have been uploaded on 01/09/2025. Analytic code will be available from September 2026 to September 2036.
• IPD Sharing Access Criteria: Please email the project PI, Professor Wendy Hall. Contact details are available in the contacts section.
• IPD Sharing Supporting Information Type: STUDY_PROTOCOL; SAP; ICF; ANALYTIC_CODE

Drug and device information, study documents

• Studies a U.S. FDA-regulated drug product: No
• Studies a U.S. FDA-regulated device product: No