Influence of the Gut Microbiome on Blueberry Polyphenol Metabolites

This study is an acute, single-arm polyphenol pharmacokinetic study designed to evaluate inter-individual variability in the metabolism of blueberry polyphenols and the role of the gut microbiome in shaping these responses. The study will be conducted at Colorado State University in the Food & Nutrition Clinical Research Laboratory. We will enroll approximately 125 healthy adults (≥18 years of age), with stratified recruitment across a range of ages and body mass index (BMI) values to capture diversity in gut microbiome composition. Participants will provide written informed consent prior to participation and will be compensated for their time.

Eligible participants will be generally healthy adults able to provide informed consent and adhere to study procedures. Key exclusion criteria include pregnancy or breastfeeding; pre-specified chronic diseases; recent antibiotic use; conditions affecting nutrient absorption; anemia; BMI ≤18.5 kg/m²; unwillingness to adhere to study protocols; recent blood draw within 1 week; participation in another research study; and contraindications to study procedures, treatments, or supplies.

The study consists of three main components: a screening visit, an acute test day, and a 24-hour follow-up visit. During the initial screening visit, participants will complete a health and medical history questionnaire, anthropometric assessments, blood pressure measurements, and a fasting blood draw to assess metabolic health and eligibility.

Following screening, participants will complete a short lead-in period prior to the test day, during which they will collect stool samples and a 24-hour urine sample at home and complete three 24-hour dietary recalls. They will also follow a low-polyphenol diet for three days prior to the test visit to minimize background variability in polyphenol exposure.

On the test day, participants will report to the laboratory following an overnight fast. Participants will consume a standardized blueberry beverage containing freeze-dried blueberry powder. Serial blood samples will be collected via an indwelling catheter at baseline and at multiple time points over an 8-hour period (0, 1, 2, 4, 6, and 8 hours) to characterize the pharmacokinetics of circulating blueberry polyphenol metabolites. Additional blood samples will be collected for peripheral blood mononuclear cell (PBMC) isolation at hours 4 and 6. Standardized low-polyphenol meals and snacks will be provided during the visit. Participants will also initiate a 24-hour urine collection and receive a stool collection kit for post-visit sampling.

Participants will return approximately 24 hours after blueberry consumption for a follow-up visit, which includes an additional fasting blood draw and return of urine and stool samples.

Throughout the study, additional data will be collected via validated questionnaires assessing gastrointestinal symptoms, sleep quality, physical activity, diet, and social determinants of health. Biological samples (blood, urine, and stool) will be used to assess polyphenol metabolism, gut microbiome composition and function, and related multi-omic profiles.

Inclusion criteria

• Healthy adults ≥18 years of age
• Able and willing to provide informed consent
• Willing and able to adhere to all study procedures and visit requirements

Exclusion criteria

• Age <18 years
• Pregnant or breastfeeding
• Presence of chronic diseases, including but not limited to cardiovascular disease, diabetes, cancer, kidney, liver, gastrointestinal, or pancreatic disease
• Use of medications for chronic diseases that may interfere with study outcomes
• Any condition known to negatively impact nutrient absorption (e.g., inflammatory bowel disease, celiac disease, gastroparesis)
• Anemia (hemoglobin <13.5 g/dL in men or <12.0 g/dL in women)
• Body mass index (BMI) ≤18.5 kg/m²
• Use of antibiotics within the past 2 months
• Recent blood draw within 1 week prior to study participation
• Currently participating in another research study involving a diet or exercise intervention
• Known allergy or contraindication to blueberry products or study procedures
• Unwilling or unable to comply with study requirements