The researchers will investigate blood and fecal responses in qualified study participants after eating walnuts for 4 weeks compared to not eating walnuts for 4 weeks. The two dietary interventions will be separated by a 4 week washout period. The order of diets will be random; study participants will complete both interventions. Dietary modifications will be part of the study protocol.
The researchers hypothesize that walnut consumption will induce changes in fecal metagenome, identifiable walnut-derived bioactives (urolithins) and other microbial-derived products (short-chain fatty acids and secondary bile acids). The researchers hypothesize that walnut consumption will result in improvements to blood lipid profiles, including decreased total and LDL-cholesterol; increased HDL-related cholesterol efflux capacity and antioxidant protection; and decreased inflammatory biomarkers relative to control diet. The researchers hypothesize changes in cardiometabolic health biomarkers will be correlated with food bioactive metabolites and/or fecal metagenome. Pathway analysis will identify metabolic pathways differentially regulated by walnut-derived bioactives and walnut-responsive microbial genes.
Study Type
INTERVENTIONAL
Allocation
RANDOMIZED
Purpose
BASIC_SCIENCE
Masking
SINGLE
Ragle Human Nutrition Research Center
Davis, California, United States
Assessing the influence of walnuts on the fecal metagenome
Changes in fecal metagenomics will be assessed via Illumina sequencing
Time frame: Through study completion, an average of 12 weeks
Assessing the influence of walnuts on fecal secondary bile acids
Fecal secondary bile acids will be measured by LC-QTOF/MS
Time frame: Through study completion, an average of 12 weeks
Assessing the influence of walnuts on fecal short-chain fatty acids
Short-chain fatty acids in fecal matter will be measured by LC-MS/MS
Time frame: Through study completion, an average of 12 weeks
Urolithins measured in plasma by UPLC/MS
Measure for changes in the levels of urolithins in separated plasma; measured in units of ug/uL. Blood will be assessed at each of the 4 study visits.
Time frame: Through study completion, an average of 12 weeks
Fecal calprotectin will be measured by ELISA
Measure for changes in the levels of calprotectin in collected fecal matter; measured in units of ug/g. Feces will be assessed at each of the 4 study visits.
Time frame: Through study completion, an average of 12 weeks
Assessing the influence of walnuts 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 at each of the 4 study visits
Time frame: Through study completion, an average of 12 weeks
Assessing the influence of walnuts on paraoxonase-1 (PON-1) activity
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Measure for changes in PON-1 activity in separated plasma at each study of the 4 study visits. Activity will be calculated based on linear rates of hydrolysis of phenyl acetate to phenol
Time frame: Through study completion, an average of 12 weeks
Assessing the influence of walnuts on cholesterol ester transfer protein activity (CETP)
Changes in CETP activity will be measured at each of the 4 study visits. The isolated plasma will be co-incubated with donor and acceptor molecules using a commercially available assay kit.
Time frame: Through study completion, an average of 12 weeks
Assessing the influence of walnuts on hsCRP will be measured in blood
hsCRP will be measured in blood at each study visit
Time frame: Through study completion, an average of 12 weeks
Assessing the influence of walnuts on SAA will be measured in blood
SAA will be measured in blood at each study visit
Time frame: Through study completion, an average of 12 weeks
Assessing the influence of walnuts on circulating cytokines
ICAM and VCAM will be measured in blood at each study visit using a commercially available ELISA kit.
Time frame: Through study completion, an average of 12 weeks
Assessing the influence of walnuts on peripheral blood mononuclear cells (PBMC) using ex vivo stimulation assays
In-vitro: media from LPS stimulated monocytes will be used to measure gene expression and cytokines Measurement of changes in PBMC derived cytokines as a marker of inflammation at each of the 4 study visits. Assessment will be based on an increase or decrease in concentration in pg/ml.
Time frame: Through study completion, an average of 12 weeks
Dietary record analysis
Use a computer program to check for study dietary requirements. Subjects are to avoid olives and olive containing products during study protocol periods. This will be done using a subject self-recorded 3-day food record submitted to study personnel.
Time frame: Through study completion, an average of 12 weeks
Anthropometric measurements
Measure waist (cm) and hip circumference (cm) before the start of drawing blood on study day protocols.
Time frame: Through study completion, an average of 12 weeks
Measure for changes in weight
Measure weight (kg) before the start of drawing blood on study day protocols
Time frame: Through study completion, an average of 12 weeks
Measure for changes in blood pressure
Measure blood pressure (mmHg) before the start of drawing blood on study day protocols
Time frame: Through study completion, an average of 12 weeks