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.
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
Allocation
RANDOMIZED
Purpose
PREVENTION
Masking
NONE
Enrollment
20
Separated, ground walnut de-fatted nut meat incorporated into inert food carrier
Walnut oil extracted from nut meat and incorporated into inert food carrier
Separated, ground walnut skins incorporated into inert food carrier
Penn State General Clinical Research Center
University Park, Pennsylvania, United States
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.
Time frame: 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).
Time frame: Change from baseline for each timepoint (60, 120, 240, 360 min)
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85g whole walnuts, ground, incorporated into inert food carrier
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.
Time frame: 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).
Time frame: 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.
Time frame: 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).
Time frame: 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.
Time frame: 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).
Time frame: Change from baseline for each timepoint (60, 120, 240, 360 min)
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.
Time frame: 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.
Time frame: 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.
Time frame: 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.
Time frame: 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.
Time frame: 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).
Time frame: 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 \[walnut skin group at 360 min (n=1), walnut oil group at 120 min (n=2), whole walnut group at 240 min(n=1)\].
Time frame: Change from baseline for each timepoint (30, 60, 120, 240, 360 min)