Prebiotic Effects of California Grapes on Gut Health and Cardiometabolic Health in Overweight Men and Women

The goal of this clinical trial is to assess the impact of table grape consumption on gut microbiome, intestinal permeability, systemic inflammation, and vascular function in healthy overweight men and women aged 45-70 years. The main questions it aims to answer are:

• Does daily grape intake alter intestinal microbiome composition and intestinal permeability?
• Are changes in gut microbiota and intestinal permeability correlated with changes in cardiometabolic risk factors (inflammation, vascular function, lipid profiles)?
• Does response to grape intake on gut microbiota, intestinal permeability, cardiometabolic and inflammatory markers differ between men and women?
• Are metabolic pathways modified by grape consumption able to explain the link between gut health and cardiometabolic factors?

Researchers will compare freeze-dried grape powder to placebo powder to see if grape powder improves cardiometabolic risk factors.

Participants will

• Consume the powder dissolved in water twice daily for 4 weeks
• Follow their usual diet, modified to limit polyphenol-rich foods
• Visit the clinic at the beginning and end of the intervention for vascular measurements and blood sample collection
• Complete a 3-day dietary recall and collect stool sample before each visit

Participants will limit intake of grapes and other polyphenol-rich foods while following their usual diet during the 3-day run-in period before the start of the intervention. They will be randomized to start with either grape or placebo powder for 4 weeks, consuming 40 grams of freeze-dried grape powder or placebo dissolved in water twice daily. Compliance will be assessed with three 24-hour dietary recalls using ASA24 and follow-up contact. After a 4-week washout period, participants will crossover to the other intervention. Study outcomes and anthropometry will be measured on the first and last days of each intervention arm.

Aim 1: Biomarkers to assess the permeability of the gut, including zonulin, lipopolysaccharide (LPS), LPS-binding protein (LBP), soluble CD14, and diamine oxidase (DAO), will be analyzed from blood samples. Gut microbiome profiling will be analyzed from 16S rRNA gene sequencing of fecal samples collected by participants at the beginning and end of each intervention arm.

Aim 2: Vascular function will be assessed by measuring blood pressure and pulse wave velocity. After 15 minutes of rest, blood pressure will be measured three times, with the average of the latter two recorded. Pulse wave velocity from the carotid to femoral artery will measure arterial stiffness. Inflammatory cytokines will be assayed from blood samples to include Th17 cytokines. Lipid panel and comprehensive metabolic panels will also be analyzed.

Aim 3: Sex differences in response to grape consumption will be assessed, including gut microbiome, gut permeability, vascular function, inflammation, lipid profile, and metabolomic pathways. Gender and time interactions will be determined to assess differences in trajectory of changes.

Aim 4: LC-MS will be used for untargeted metabolomics and lipidomics. Pathway analysis will assess metabolic pathways affected by grape consumption and their links to gut permeability, systemic inflammation, and vascular function.