Response of Cardiometabolic Biomarkers and Gut Microbiota to Walnut Consumption

Study Overview
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Brief Summary
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The purpose of this research is to test if eating walnuts will cause any changes in blood lipids (like good and bad cholesterol, for example) and levels of inflammation in the blood, as well as changes in the bacteria living in the gut.

Detailed Description
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The purpose of this research is to test if eating walnuts will cause any changes in blood lipids (like good and bad cholesterol, for example) and levels of inflammation in the blood, as well as changes in the bacteria living in the gut. Overweight/obese adults between the ages of 45 and 70 yo with elevated LDL-C levels are eligible to participate. The study involves 5 visits (1 initial screening and 4 study visits) and will last about 10 weeks. There is a 1-week run-in period before starting the study, followed by two diet intervention periods each lasting 3 weeks, separated by a 3-week washout period. Participation in this study will involve an initial 1-week run in period to become accustomed to the study diet. After this 1 week period, participants will be randomly selected to start either a walnut or a no-nut diet. During each phase of the study, participants will be asked to come to the University of California, Davis campus after a 10-12 hour overnight fast. At each visit, body measurements will be taken; blood, urine and fecal samples will be collected. During the 10 weeks of the study, all nuts and nut-derived products will need to be avoided. The study will provide walnuts to be eaten at home for each intervention phase. Additionally, the investigators will ask that ellagitannin-rich foods, high-fiber and fermented foods be avoided in the diet. Detailed food diaries will be filled out and brought to study visits.

Official Title
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Response of Cardiometabolic Biomarkers and Gut Microbiota to Walnut Consumption

Conditions
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Cardiovascular Diseases

Intervention / Treatment
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* Dietary Supplement: Walnuts
* Dietary Supplement: No-nut diet


Participation Criteria
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Eligibility Criteria
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Inclusion Criteria: Overweight and obese men and postmenopausal women between 45-70 years of age, BMI range of 25.0-39.9 kg/m2 and elevated LDL-C levels (130-189 mg/dL). Exclusion Criteria: Adults unable to consent, individuals who are not yet adults (infants, children, teenagers), pregnant or lactating women, women planning to become pregnant in the next four months and prisoners will be specifically excluded. Additional exclusion criteria are listed below: Allergy to walnuts or other nuts Eating more than 25 grams of fiber per day, assessed by the Block Dietary-Fruit-Vegetable-Fiber Screener© Taking medications or supplements known to affect metabolism or gut microbiota composition (i.e. Metformin, statins, antibiotics within the past 3 months, fiber supplements, probiotics, and others) Documented chronic diseases including diabetes, renal or liver disease, metabolic syndrome, active cancer, MI or stroke, history of gastric bypass or GI disease (e.g. Crohn's Disease, Irritable Bowel Disease, diverticulosis, diverticulitis, etc.) Smoker or living with a smoker, including vaporizer and/or electronic cigarettes. Illicit drug use, cannabis usage, or consuming >1 alcoholic drink/day Extreme dietary or exercise patterns Recent weight fluctuations (>10% in the last 6 months) Taking prescription lipid medications or supplements that may affect lipoprotein metabolism (i.e. >1 g of fish oil/day, antioxidant supplements) Taking exogenous hormones Poor venous access Unwillingness to comply with study protocols

Ages Eligible for Study
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Minimum Age: 45 Years
Maximum Age: 70 Years

Sexes Eligible for Study
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All

Accepts Healthy Volunteers
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No

Study Plan
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How is the study designed?
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Design Details

Primary Purpose: Basic Science
Allocation: Randomized
Intervention Model: Crossover Assignment
Masking: None (Open Label)


Arms and Interventions

| Participant Group/Arm | Intervention/Treatment |
| --- | --- |
| Active Comparator: Walnut diet<br>Participants will consume 56 g of walnuts each day at home for 3 weeks. | Dietary Supplement: Walnuts<br>* Participants will consume 56 g of walnuts daily for 3 weeks. Participants will also follow a diet devoid of ellagitannin-rich, high fiber, and fermented foods.<br>|
| Active Comparator: No-nut diet<br>Participants will follow a no-nut diet for 3 weeks. | Dietary Supplement: No-nut diet<br>* Participants will exclude all nuts and nut-derived products; high-fiber, fermented and ellagitannin-rich foods will also be excluded.<br>|

What is the study measuring?
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Primary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Assessing the influence of walnut consumption on blood lipid measurements. | Measure for changes in the levels of HDL and LDL in separated plasma; measured in units of mg/dL. Blood will be assessed for the fasting (baseline) sample at each of the 4 study visits. | Through study completion, an average of 10 weeks | 
| Assessing the influence of walnut consumption on circulating inflammatory markers: PAI-1, VCAM-1 and ICAM-1. | Measure circulating inflammatory markers in separated plasma at each of the 4 study visits. Commercially available ELISA kits will be used: PAI-1, VCAM-1, ICAM-1. | Through study completion, an average of 10 weeks | 
| Assessing the influence of walnut consumption on blood pressure. | Measure blood pressure (mmHg) before the start of drawing blood on study day protocols. | Through study completion, an average of 10 weeks | 

Secondary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Assessing the influence of walnut consumption on fecal pH. | Measure fecal pH via pH meter at each of the 4 study visits. | Through study completion, an average of 10 weeks | 
| Assessing the influence of walnut consumption on stool consistency. | Assess fecal consistency using Bristol Stool Scale at each of the 4 study visits. The scale runs from Type 1 (the lowest) to Type 7 (the highest). The desirable Type is either 3 or 4. Types 1 and 2 may be indicative of constipation, while Types 5, 6, and 7 may indicative diarrhea. | Through study completion, an average of 10 weeks | 
| Assessing the influence of walnut consumption on fecal moisture. | Measure fecal moisture by weighing wt and vacuum dried feces in grams at each of the 4 study visits. | Through study completion, an average of 10 weeks | 
| Assessing the influence of walnut consumption on the levels of gut inflammatory markers: Lipocalin-2 and calprotectin. | Measure fecal levels of Lipocalin-2 and calprotectin at each of the 4 study visits. Commercially available ELISA kits will be used: lipocalin-2, calprotectin. | Through study completion, an average of 10 weeks | 
| Assessing the influence of walnut consumption on plasma and urine levels of walnut-derived metabolites - urolithins. | Measure urolithin levels in separated plasma and urine via metabolomics analysis at each of the 4 study visits. | Through study completion, an average of 10 weeks | 

 Terms related to the study
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Keywords Provided by Centre Hospitalier Valida
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gut health, heart health, gut microbiota, Mediterranean diet, cardiometabolic health, diet