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

Participants will limit intake of grapes and other polyphenol-rich foods while following their usual diet during the 1-week run-in period before the start of the intervention. They will be randomized to start with either grape or placebo powder for 3 weeks, consuming 48 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 3- to 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.

Inclusion criteria

• post-menopausal women (cessation of menstruation for minimum two years)
• overweight and obese (BMI between 25-35 kg/m2)
• stable treatment for type 2 diabetes or metabolic syndrome
• ability to understand the intervention concept and written consent to participate
• willingness to accept randomization, undergo testing and intervention procedures, and deliver stool and blood samples

Exclusion criteria

• menopausal hormone replacement therapy started within less than 6 months
• antibiotics, prebiotics within last 3 months
• antidiabetic treatment involving insulin (for type 1 diabetes)
• vegetarian/vegan and not able to follow modified diet
• any serious medical condition including but not limited to coronary artery disease, uncontrolled hypertension, stroke, congestive heart failure, insulin-dependent diabetes, liver disease, active cancer and anemia
• psychiatric disease that interferes with the understanding and implementation of the intervention
• history of eating disorders such as bulimia nervosa, anorexia nervosa, severe binge eating disorder in the last 5 years
• history of substance abuse or alcohol abuse
• involvement in a weight loss intervention program (including anti-obesity medication) within last 3 months or have had bariatric surgery
• current smokers (within last 180 days)
• use of dietary supplements containing polyphenols in the past 1 month
• strenuous exercise greater than 10 hours per week