Postprandial Effects of Walnut Components Versus Whole Walnuts on Cardiovascular Disease (CVD) Risk Reduction

Postprandial Effects of Walnut Components vs Whole Walnuts on Oxidative Stress, Inflammation, Platelet Function, and Endothelial Function in Volunteers With Moderate Hypercholesterolemia

The purpose of this study is to evaluate the acute, postprandial effects and mechanism of action of various walnut components (separated nut skins, de-fatted nut meat, nut oil) versus whole walnuts on oxidative stress, inflammation and measures of platelet and endothelial function in healthy adults with moderately elevated cholesterol levels.

Study Overview

• Status: Completed
• Conditions: Cardiovascular Disease
• Intervention / Treatment: Dietary supplement: Whole walnut; Dietary supplement: Walnut "meat"; Dietary supplement: Walnut Oil; Dietary supplement: Walnut Skins

Detailed Description

Walnuts contain high contents of polyunsaturated fatty acids (PUFA), particularly linoleic acid and linolenic acid. The high PUFA content has been suggested to reduce CVD risk through decreasing total and LDL-cholesterol concentrations, and increasing HDL-C concentrations. In addition, walnuts are rich in substances such as ellagic acid (a polyphenol), antioxidants, vitamin E, fiber, essential fatty acids, flavanoids, and phenolic acids. Polyphenolic compounds are believed to have multiple biological effects influencing oxidative stress, platelet function, inflammation, and cancer initiation and propagation. There is interest in identifying foods with these and other favorable compounds to test their efficacy in real world settings to further understand their role in the human diet. Despite positive benefits found in consumption of the walnuts, it is not known which specific component of the walnut (i.e., whole walnut, walnut skin, defatted walnut, or walnut oil) is most beneficial to health. The investigators hypothesize that maximum improvements in oxidative stress, inflammatory markers, platelet and endothelial function will be observed following consumption of the whole nut versus isolated walnut components, thereby leading to a recommendation to consume walnuts. In addition, results from the research proposed will provide new information about the antioxidant, inflammatory, platelet activity and endothelial effects of the different walnut components and the synergistic effects these components have in the postprandial state.

• Study Type: Interventional
• Enrollment (Actual): 20
• Phase: Not Applicable

Contacts and Locations

Study Locations

• United States
  • Pennsylvania
    • University Park, Pennsylvania, United States, 16802
      • Penn State General Clinical Research Center

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: 21 years to 60 years (Adult)
• Accepts Healthy Volunteers: Yes

Description

Inclusion Criteria:

• Age 21 - 60 years
• Body mass index 25-39 kg/m2
• LDL cholesterol >110 mg/dL
• <95 percentile for age and gender for both (based on NHANES data)
• TG < 350 mg/dL

Exclusion Criteria:

• High alcohol consumption > 21 units/week (female subjects) or > 28 units/week (male subjects)
• Intake of vitamin and mineral supplements within the past 3 weeks or unwillingness to discontinue for 3 weeks prior to screening and for entire study.
• Use of prescription cholesterol-lowering or blood pressure-lowering medications during the study
• Intake of other putative cholesterol-lowering supplements (excl. psyllium, fish oil capsules, soy lecithin, phytoestrogens)
• Intake of anti-inflammatory medications (containing aspirin or NSAIDS) on a regular basis or if an acute intake, within 48 hours of a test day
• Diabetes, liver, kidney, thyroid (unless controlled and stable on replacement medication) or other endocrine disorders from self-reported medical history
• Treatment with drugs acting on the gut, such as ezetimibe, bile acid-binding resins, orlistat
• Dietary restrictions such as a medically prescribed diet, or a slimming diet prior to or during the trial
• Weight loss or gain of 10% body weight or more during a period of 6 months before pre-study examination.
• Blood/plasma donation for reason(s) other than the present study prior to the study (1 month for a male subject or 2 months for a female subject), or during the study
• Lactation 6 weeks before the start of and during study, pregnant or wishing to become pregnant 3 months before or during the study

Study Plan

How is the study designed?

Design Details

• Primary Purpose: Prevention
• Allocation: Randomized
• Interventional Model: Crossover Assignment
• Masking: None (Open Label)

Number of Arms

4

Arms and Interventions

Participant Group / Arm	Intervention / Treatment
Experimental: Whole walnut; 85g whole walnuts, ground, incorporated into inert food carrier	Dietary supplement: Whole walnut; 85g whole walnuts, ground, incorporated into inert food carrier
Experimental: Walnut "meat"; Separated, ground walnut de-fatted nut meat incorporated into inert food carrier	Dietary supplement: Walnut "meat"; Separated, ground walnut de-fatted nut meat incorporated into inert food carrier
Experimental: Walnut oil; Walnut oil extracted from nut meat and incorporated into inert food carrier	Dietary supplement: Walnut Oil; Walnut oil extracted from nut meat and incorporated into inert food carrier
Experimental: Walnut skins; Separated, ground walnut skins incorporated into inert food carrier	Dietary supplement: Walnut Skins; Separated, ground walnut skins incorporated into inert food carrier

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Main Effect of Treatment on the Ferric Reducing Antioxidant Potential (FRAP) Changes in Response to 4 Walnut Treatments	On the day of each test, participants arrived at the General Clinical Research Center after a 12-h overnight fast. A baseline (0 min) fasting blood sample was collected. Participants then had 15 min to consume 1 of the 4 walnut test meals. Blood samples (∼30 mL) were subsequently taken at 30, 60, 120, 240, and 360 min following the meal and FRAP was measured at 0, 60, 120, 240, and 360 min. The FRAP assay was used to determine the reducing ability of plasma in a redox-linked colorimetric reaction. Plasma was incubated with the FRAP reagent at room temperature for 1 h and the absorbance at 593 nm was then recorded. Trolox was used as a reference to construct a standard curve to calculate the FRAP value of the samples. The FRAP assay measures lipophilic and hydrophilic antioxidants (total antioxidant capacity), both of which are present in walnuts.	AUC values were calculated with the trapezoidal rule, using the respective fasting baseline value as the line of reference. Measured at 0 to 360 min (baseline to 360min post meal) for each of the 4 walnut treatments.
Main Effect of Treatment by Timepoint on the Ferric Reducing Antioxidant Potential (FRAP) Changes in Response to 4 Walnut Treatments	On the day of each test, participants arrived at the General Clinical Research Center after a 12-h overnight fast. A baseline (0 min) blood sample was collected. Participants then had 15 min to consume 1 of 4 walnut test meals. Blood samples (∼30 mL) were subsequently taken at 30, 60, 120, 240, and 360 min following the meal and FRAP was measured at 0, 60, 120, 240, and 360 min. The FRAP assay was used to determine the reducing ability of plasma in a redox-linked colorimetric reaction. Plasma was incubated with the FRAP reagent at room temperature for 1 h and the absorbance at 593 nm was then recorded. Trolox was used as a reference to construct a standard curve to calculate the FRAP value of the samples. The FRAP assay measures lipophilic and hydrophilic antioxidants (total antioxidant capacity), both of which are present in walnuts. Several blood samples (n=3) could not be obtained/measured (walnut skin group at 360 min, walnut oil group at 120 min, whole walnut group at 240 min).	Change from baseline for each timepoint (60, 120, 240, 360 min)
Main Effect of Treatment on the Changes in Total Thiol Response to 4 Walnut Treatments	On the day of each test, participants arrived at the General Clinical Research Center after a 12-h overnight fast. A baseline (0 min) fasting blood sample was collected. Participants then had 15 min to consume 1 of the 4 walnut test meals. Blood samples (∼30 mL) were subsequently taken at 30, 60, 120, 240, and 360 min following the meal and total thiols measured at 0, 60, 120, 240, and 360 min. Total thiols in plasma were determined by the following methods: an aliquot of EDTA plasma was mixed with Tris-EDTA buffer, followed by addition of 10 mmol/L 2,2-dithiobisnitrobenzoic acid and methanol. After incubation at room temperature for 15 min and centrifugation, the absorbance of the supernatant was measured at 412 nm.	AUC values were calculated with the trapezoidal rule, using the respective fasting baseline value as the line of reference. Measured at 0 to 360 min (baseline to 360min post meal) for each of the 4 walnut treatments.
Main Effect of Treatment by Timepoint on Total Thiol Changes in Response to 4 Walnut Treatments	On the day of each test, participants arrived at the General Clinical Research Center after a 12-h overnight fast. A baseline (0 min) fasting blood sample was collected. Participants then had 15 min to consume 1 of the 4 walnut test meals. Blood samples (∼30 mL) were subsequently taken at 30, 60, 120, 240, and 360 min following the meal and total thiols measured at 0, 60, 120, 240, and 360 min. Total thiols in plasma were determined by the following methods: an aliquot of EDTA plasma was mixed with Tris-EDTA buffer, followed by addition of 10 mmol/L 2,2-dithiobisnitrobenzoic acid and methanol. After incubation at room temperature for 15 min and centrifugation, the absorbance of the supernatant was measured at 412 nm. Several blood samples (n=3) could not be obtained/measured (walnut skin group at 360 min, walnut oil group at 120 min, whole walnut group at 240 min).	Change from baseline for each timepoint (60, 120, 240, 360 min)
Main Effect of Treatment on the Changes in Malondialdehyde (MDA) Response to 4 Walnut Treatments	On the day of each test, participants arrived at the General Clinical Research Center after a 12-h overnight fast. A baseline (0 min) fasting blood sample was collected. Participants then had 15 min to consume 1 of the 4 walnut test meals. Blood samples (∼30 mL) were subsequently taken at 30, 60, 120, 240, and 360 min following the meal and MDA measured at 0, 60, 120, 240, and 360 min. Plasma MDA was measured by an Agilent 1100 HPLC system with fluorometric detection.	AUC values were calculated with the trapezoidal rule, using the respective fasting baseline value as the line of reference. Measured at 0 to 360 min (baseline to 360min post meal) for each of the 4 walnut treatments.
Main Effect of Treatment by Timepoint on Malondialdehyde (MDA) Changes in Response to 4 Walnut Treatments	On the day of each test, participants arrived at the clinic after a 12-h overnight fast. A baseline (0 min) blood sample was collected. Participants then had 15 min to consume 1 of the 4 walnut test meals. Blood samples (∼30 mL) were subsequently taken at 30, 60, 120, 240, and 360 min following the meal and MDA measured at 0, 60, 120, 240, and 360 min. Plasma MDA was measured by an Agilent 1100 HPLC system with fluorometric detection. Several blood samples (n=2) could not be obtained (walnut oil group at 120 min and whole walnut group at 240 min).	Change from baseline for each timepoint (60, 120, 240, 360 min)
Main Effect of Treatment on the Changes in C-reactive Protein (CRP) Response to 4 Walnut Treatments	On the day of each test, participants arrived at the General Clinical Research Center after a 12-h overnight fast. A baseline (0 min) fasting blood sample was collected. Participants then had 15 min to consume 1 of the 4 walnut test meals. Blood samples (∼30 mL) were subsequently taken at 30, 60, 120, 240, and 360 min following the meal and CRP measured at 0, 60, 120, 240, and 360 min. Serum CRP was measured by latex-enhanced immunonephelometry.	AUC values were calculated with the trapezoidal rule, using the respective fasting baseline value as the line of reference. Measured at 0 to 360 min (baseline to 360min post meal) for each of the 4 walnut treatments.
Main Effect of Treatment by Timepoint on C-reactive Protein (CRP) Changes in Response to 4 Walnut Treatments	On the day of each test, participants arrived at the General Clinical Research Center after a 12-h overnight fast. A baseline (0 min) fasting blood sample was collected. Participants then had 15 min to consume 1 of the 4 walnut test meals. Blood samples (∼30 mL) were subsequently taken at 30, 60, 120, 240, and 360 min following the meal and CRP measured at 0, 60, 120, 240, and 360 min. Serum CRP was measured by latex-enhanced immunonephelometry. Several blood samples (n=3) could not be obtained/measured (walnut oil/120 min, whole walnut/240 min, and walnut skin/360 min).	Change from baseline for each timepoint (60, 120, 240, 360 min)

Secondary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Main Effect of Treatment on Reactive Hyperemia Index (RHI) Changes in Response to 4 Walnut Treatments	On the day of each test, participants arrived at the General Clinical Research Center after a 12-h overnight fast. At baseline the endothelial function test was performed using pulse amplitude tonometry (PAT) (Itamar Medical). Participants then had 15 min to consume 1 of the 4 walnut test meals. The endothelial function test was performed again at 240 min postmeal. RHI was calculated as the ratio of the average pulse wave amplitude during hyperemia (60 to 120 s of the post occlusion period) to the average pulse wave amplitude during baseline in the occluded hand divided by the same values in the control hand and then multiplied by a baseline correction factor. No endothelial function test data available for one participant within the walnut oil group and one within the defatted walnut nutmeat group.	Change from baseline at 240 min
Main Effect of Treatment on Framingham Reactive Hyperemia Index (fRHI) Changes in Response to 4 Walnut Treatments	On the day of each test, participants arrived at the General Clinical Research Center after a 12-h overnight fast. At baseline the endothelial function test was performed using pulse amplitude tonometry (PAT) (Itamar Medical). Participants then had 15 min to consume 1 of the 4 walnut test meals. The endothelial function test was performed again at 240 min postmeal. fRHI is an alternative calculation derived from the same raw data (as RHI) and differs in that it uses the period from 90 to 120 s of postocclusion hyperemia, does not incorporate a baseline correction factor, and has a natural log transformation applied to the resulting ratio. No endothelial function test data available for one participant within the walnut oil group and one within the defatted walnut nutmeat group.	Change from baseline at 240 min
Main Effect of Treatment on Heart Rate (HR) Changes in Response to 4 Walnut Treatments	On the day of each test, participants arrived at the General Clinical Research Center after a 12-h overnight fast. At baseline the endothelial function test was performed using pulse amplitude tonometry (PAT) (Itamar Medical). Participants then had 15 min to consume 1 of the 4 walnut test meals. The endothelial function test was performed again at 240 min postmeal. No endothelial function test data available for one participant within the walnut oil group and one within the defatted walnut nutmeat group.	Change from baseline at 240 min
Main Effect of Treatment on Augmentation Index (AI) Changes in Response to 4 Walnut Treatments	On the day of each test, participants arrived at the General Clinical Research Center after a 12-h overnight fast. At baseline the endothelial function test was performed using pulse amplitude tonometry (PAT) (Itamar Medical). Participants then had 15 min to consume 1 of the 4 walnut test meals. The endothelial function test was performed again at 240 min postmeal. AI is a measure of vascular stiffness (pulse wave reflection) that is calculated from the shape of the pulse wave recorded during baseline. No endothelial function test data was available for one participant within the walnut oil group and one within the defatted walnut nutmeat group.	Change from baseline at 240 min
Main Effect of Treatment on Augmentation Index Standardized to a Heart Rate of 75 Beats/Min (AI_75) Changes in Response to 4 Walnut Treatments	On the day of each test, participants arrived at the General Clinical Research Center after a 12-h overnight fast. At baseline the endothelial function test was performed using pulse amplitude tonometry (PAT) (Itamar Medical). Participants then had 15 min to consume 1 of the 4 walnut test meals. The endothelial function test was performed again at 240 min postmeal. AI is a measure of vascular stiffness (pulse wave reflection) that is calculated from the shape of the pulse wave recorded during baseline. AI can be adjusted to a heart rate of 75 beats/min (AI_75) to correct for the independent effect of heart rate on this measure.No endothelial function test data was available for one participant within the walnut oil group and one within the defatted walnut nutmeat group.	Change from baseline at 240 min
Main Effect of Treatment on the Triglyceride (TG) Changes in Response to 4 Walnut Treatments	On the day of each test, participants arrived at the General Clinical Research Center after a 12-h overnight fast. A baseline (0 min) fasting blood sample was collected. Participants then had 15 min to consume 1 of the 4 walnut test meals. Blood samples (∼30 mL) were subsequently taken at 30, 60, 120, 240, and 360 min following the meal and TG was measured at 0, 30, 60, 120, 240, and 360 min. TG were determined by standard colorimetric and enzymatic procedures with commercially available kits (Alfa Wassermann).	AUC values were calculated with the trapezoidal rule, using the respective fasting baseline value as the line of reference. Measured at 0 to 360 min (baseline to 360min post meal) for each of the 4 walnut treatments.
Main Effect of Treatment by Timepoint on Triglyceride (TG) Changes in Response to 4 Walnut Treatments	On the day of each test, participants arrived at the General Clinical Research Center after a 12-h overnight fast. A baseline (0 min) fasting blood sample was collected. Participants then had 15 min to consume 1 of the 4 walnut test meals. Blood samples (∼30 mL) were subsequently taken at 30, 60, 120, 240, and 360 min following the meal and TG was measured at 0, 30, 60, 120, 240, and 360 min. TG were determined by standard colorimetric and enzymatic procedures with commercially available kits (Alfa Wassermann). Several blood samples (n=4) could not be obtained/measured [walnut skin group at 360 min (n=1), walnut oil group at 120 min (n=2), whole walnut group at 240 min(n=1)].	Change from baseline for each timepoint (30, 60, 120, 240, 360 min)

Collaborators and Investigators

• Sponsor: Penn State University
• Collaborators: California Walnut Commission
• Investigators: Principal Investigator: Penny M Kris-Etherton, PhD, Penn State University

Publications and helpful links

General Publications

• Berryman CE, Grieger JA, West SG, Chen CY, Blumberg JB, Rothblat GH, Sankaranarayanan S, Kris-Etherton PM. Acute consumption of walnuts and walnut components differentially affect postprandial lipemia, endothelial function, oxidative stress, and cholesterol efflux in humans with mild hypercholesterolemia. J Nutr. 2013 Jun;143(6):788-94. doi: 10.3945/jn.112.170993. Epub 2013 Apr 24.
• Zhang J, Grieger JA, Kris-Etherton PM, Thompson JT, Gillies PJ, Fleming JA, Vanden Heuvel JP. Walnut oil increases cholesterol efflux through inhibition of stearoyl CoA desaturase 1 in THP-1 macrophage-derived foam cells. Nutr Metab (Lond). 2011 Aug 26;8:61. doi: 10.1186/1743-7075-8-61.

Study record dates

Study Major Dates

• Study Start: August 1, 2007
• Primary Completion (Actual): February 1, 2009
• Study Completion (Actual): May 1, 2009

Study Registration Dates

• First Submitted: June 18, 2009
• First Submitted That Met QC Criteria: July 10, 2009
• First Posted (Estimated): July 13, 2009

Study Record Updates

• Last Update Posted (Actual): August 21, 2023
• Last Update Submitted That Met QC Criteria: August 16, 2023
• Last Verified: August 1, 2023

More Information

Terms related to this study

• Keywords: Cardiovascular Disease
• Additional Relevant MeSH Terms: Cardiovascular Diseases
• Other Study ID Numbers: PKE 102