Mediterranean Diet and Blood Sugar Study

Glycemic Effects of a Mediterranean-Style Dietary Pattern Containing Potatoes in Adults With Prediabetes

The purpose of this research study is to determine if a healthy Mediterranean diet containing one medium potato/day has equivalent or non-different effects on risk factors for type 2 diabetes and heart disease compared to a healthy Mediterranean diet without potatoes in adults with prediabetes. Participants will be randomly assigned to one of the test diets and be asked to consume this diet for 12 weeks (84 days). Testing will be conducted at the beginning and end of the study.

Study Overview

• Status: Not yet recruiting
• Conditions: Prediabetes
• Intervention / Treatment: Other: Mediterranean-style diet with potatoes; Other: Traditional-style Mediterranean diet

Detailed Description

This is a 12-week, 2-arm parallel, randomized controlled feeding trial. Participants will be randomized to either a Mediterranean-style diet that includes 1 medium potato/day/2000 kcal replacing some grains , or a traditional-style Mediterranean dietary pattern without potatoes. All food will be provided for the 12-week study duration.

• Study Type: Interventional
• Enrollment (Estimated): 74
• Phase: Not Applicable

Contacts and Locations

• Study Contact: Name: Kristina Petersen, PhD; Phone Number: 814-865-7206; Email: kup63@psu.edu
• Study Contact Backup: Name: Stacey Meily; Phone Number: 814-863-8622; Email: sas117@psu.edu

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: Adult; Older Adult
• Accepts Healthy Volunteers: No

Description

Inclusion Criteria:

• Age 25-65 years
• Prediabetes assessed by an HbA1c of 5.7-6.4% or fasting glucose 100-125 mg/dL at screening
• BMI 25-40 kg/m2 at screening

Exclusion Criteria:

• HbA1c ≥6.5% at screening
• LDL-C (calculated with the Martin-Hopkins equation) ≥190 mg/dL at screening
• Hemoglobin <13.2 g/dL at screening

• Fasting triglycerides >350 mg/dL at screening

  -≥10% change in body weight within the 6 months prior to enrollment

• Blood pressure >140/90 mmHg at screening
• Type 1 or type 2 diabetes
• Prescription of anti-hypertensive, lipid-lowering, or glucose-lowering drugs
• Intake of supplements that affect the outcomes of interest (i.e., lipid, blood pressure, or glucose lowering; vitamin C or multi-vitamins containing vitamin C) and are unwilling to cease during the study period.
• History of liver, kidney, or autoimmune disease
• Prior cardiovascular event (e.g., stroke, heart attack)
• Current pregnancy or intention of pregnancy within the next 6 months
• Lactation within the prior 6 months
• Allergy/intolerance/sensitivity/dislike of any foods in the study menus
• Antibiotic use within the prior 1 month
• Oral steroid use within the prior 1 month
• Use of tobacco or nicotine-containing products within the past 6 months
• History of cancer at any site within the past 10 years (eligible if ≥10 years without recurrence) or non-melanoma skin cancer within the past 5 years (eligible if ≥5 years without recurrence)
• Participation in another clinical trial within 60 days of baseline
• Currently following a restricted or weight-loss diet
• Prior bariatric surgery
• Intake of >14 alcoholic drinks/week and/or not willing to avoid alcohol consumption for 48 hours prior to test visits
• Principal Investigator discretion related to the potential participant's ability to adhere to the study requirements, including being able to come to attend visits
• Does not speak and/or understand English
• Unwilling to refrain from donating blood during the study
• Weight <110 lb

Study Plan

How is the study designed?

Design Details

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

Number of Arms

2

Arms and Interventions

Participant Group / Arm	Intervention / Treatment
Experimental: Mediterranean-style diet with potato (MED-P); Mediterranean-style diet that includes 1 medium potato/day/2000 kcal replacing some grains	Other: Mediterranean-style diet with potatoes; The diet will contain 1 medium potato/day/2000 kcal
Active Comparator: Traditional-style Mediterranean dietary pattern (MED); A traditional-style Mediterranean diet that does not contain potatoes (potatoes are not a defining feature of this diet) and is higher in grains.	Other: Traditional-style Mediterranean diet; Traditional-style Mediterranean diet higher in grains

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Change in HbA1c	HbA1c will be assessed at baseline and 12-weeks and expressed as percentage . The change in HbA1c will be calculated by subtracting the baseline value from the 12 week value and expressed as percentage point change.	12-weeks

Secondary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Change in fasting glucose	Change in fasting plasma glucose expressed as mg/dL. Change in glucose will be calculated as the mean of the 12 week measures (i.e., mean of day 1 and day 2 values) minus the mean of the baseline measures (i.e., mean of day 1 and day 2 values).	12-weeks
Change in mean glucose	Change in mean glucose assessed by a continuous glucose monitor (CGM) expressed as mg/dL. Change in mean glucose will be calculated as mean glucose assessed from 7 days of CGM wear at 12 weeks minus mean glucose assessed from 7 days of CGM wear at baseline.	12-weeks
Change in mean time in range	Change in mean time in range (glucose 70-140 mg/dL) assessed by a continuous glucose monitor (CGM) expressed as minutes per day. Change in mean time in range will be calculated as mean time in range assessed from 7 days of CGM wear at 12 weeks minus mean time in range assessed from 7 days of CGM wear at baseline.	12-weeks
Change in glycemic variability	Change in mean glycemic variability assessed by a continuous glucose monitor (CGM) expressed as the coefficient of variability. Change in mean glycemic variability will be calculated as mean glycemic variability assessed from 7 days of CGM wear at 12 weeks minus mean glycemic variability assessed from 7 days of CGM wear at baseline.	12-weeks
Change in fasting insulin	Change in fasting serum insulin expressed as micro IU/mL. Change in insulin will be calculated as the mean of the 12 week measures (i.e., mean of day 1 and day 2 values) minus the mean of the baseline measures (i.e., mean of day 1 and day 2 values).	12-weeks
Change in homeostatic model of insulin resistance (HOMA-IR)	Homeostatic model of insulin resistance (HOMA-IR) will be calculated from insulin and glucose measured from a fasting blood sample. Calculated as (insulin × glucose) / 22.5. Change in HOMA-IR will be calculated as the mean of the 12 week measures (i.e., mean of day 1 and day 2 values) minus the mean of the baseline measures (i.e., mean of day 1 and day 2 values).	12-weeks
Change in LDL-Cholesterol	Assessed from fasting blood draw expressed in mg/dL. Change in LDL-cholesterol will be calculated as the mean of the 12-week measures (i.e., mean of day 1 and day 2 values) minus the mean of the baseline measures (i.e., mean of day 1 and day 2 values).	12-weeks
Change in apolipoprotein B	Assessed from fasting blood draw expressed in mg/dL. Change in apolipoprotein B will be calculated by subtracting the baseline value from the 12 week value.	12-weeks
Change in non-HDL cholesterol	Assessed from fasting blood draw expressed in mg/dL. Change in non-HDL cholesterol will be calculated as the mean of the 12-week measures (i.e., mean of day 1 and day 2 values) minus the mean of the baseline measures (i.e., mean of day 1 and day 2 values).	12-weeks
Change in Total Cholesterol	Assessed from fasting blood draw expressed in mg/dL. Change in total cholesterol will be calculated as the mean of the 12-week measures (i.e., mean of day 1 and day 2 values) minus the mean of the baseline measures (i.e., mean of day 1 and day 2 values).	12-weeks
Change in HDL-Cholesterol	Assessed from fasting blood draw expressed in mg/dL. Change in HDL-cholesterol will be calculated as the mean of the 12-week measures (i.e., mean of day 1 and day 2 values) minus the mean of the baseline measures (i.e., mean of day 1 and day 2 values).	12-weeks
Change in Triglycerides	Assessed from fasting blood draw expressed in mg/dL. Change in triglycerides will be calculated as the mean of the 12-week measures (i.e., mean of day 1 and day 2 values) minus the mean of the baseline measures (i.e., mean of day 1 and day 2 values).	12-weeks
Change in C-reactive protein	Assessed from fasting blood draw expressed in mg/L. Change in C-reactive protein will be calculated as the mean of the 12-week measures (i.e., mean of day 1 and day 2 values) minus the mean of the baseline measures (i.e., mean of day 1 and day 2 values).	12-weeks
Change in Central Systolic and Diastolic Blood Pressure	Central blood pressure measured assessed using a SphymoCor Xcel (Atcor Medical) at baseline & 12 weeks. Change will be calculated by subtracting the baseline value from the end point value.	12-weeks
Change in Peripheral Systolic and Diastolic Blood Pressure	Peripheral blood pressure measured assessed using a SphymoCor Xcel (Atcor Medical) at baseline & 12 weeks. Change will be calculated by subtracting the baseline value from the end point value.	12-weeks
Change in Carotid-Femoral Pulse Wave Velocity	Measured assessed using a SphymoCor Xcel (Atcor Medical) at baseline & 12 weeks. Change will be calculated by subtracting the baseline value from the end point value.	12-weeks
Change in particle size and number of LDL, HDL, triglyceride rich lipoproteins	Measured via Nuclear Magnetic Resonance	12-weeks
Diet Satisfaction	Participants will complete a survey that we have previously developed to assess diet satisfaction at 12 weeks.	12-weeks

Collaborators and Investigators

• Sponsor: Penn State University
• Collaborators: Alliance for Potato Research & Education

Study record dates

Study Major Dates

• Study Start (Estimated): June 1, 2026
• Primary Completion (Estimated): April 30, 2028
• Study Completion (Estimated): April 30, 2028

Study Registration Dates

• First Submitted: November 13, 2025
• First Submitted That Met QC Criteria: November 13, 2025
• First Posted (Actual): November 17, 2025

Study Record Updates

• Last Update Posted (Actual): April 2, 2026
• Last Update Submitted That Met QC Criteria: April 1, 2026
• Last Verified: April 1, 2026

More Information

Terms related to this study

• Keywords: nutrition; cardiovascular disease; diet; prediabetes; Mediterranean diet
• Additional Relevant MeSH Terms: Endocrine System Diseases; Metabolic Diseases; Glucose Metabolism Disorders; Diabetes Mellitus; Nutritional and Metabolic Diseases; Cardiovascular Diseases; Prediabetic State
• Other Study ID Numbers: MDP

Plan for Individual participant data (IPD)

• Plan to Share Individual Participant Data (IPD)?: YES
• IPD Sharing Time Frame: The SAP and protocol will be posted on clinicaltrials.gov prior to enrollment commencing.
• IPD Sharing Supporting Information Type: STUDY_PROTOCOL; SAP

Drug and device information, study documents

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