Replacing Saturated Fat With Walnuts or Vegetable Oils Improves Central Blood Pressure and Serum Lipids in Adults at Risk for Cardiovascular Disease: A Randomized Controlled-Feeding Trial

Abstract

Background Walnuts have beneficial effects on cardiovascular risk factors, but it is unclear whether these effects are attributable to the fatty acid ( FA ) content, including α-linolenic acid ( ALA ), and/or bioactives. Methods and Results A randomized, controlled, 3-period, crossover, feeding trial was conducted in individuals at risk for cardiovascular disease (n=45). Following a 2-week standard Western diet run-in (12% saturated FAs [ SFA ], 7% polyunsaturated FAs, 12% monounsaturated FAs), participants consumed 3 isocaloric weight-maintenance diets for 6 weeks each: a walnut diet ( WD ; 7% SFA , 16% polyunsaturated FAs, 3% ALA , 9% monounsaturated FAs); a walnut FA -matched diet; and an oleic acid-replaced- ALA diet (7% SFA , 14% polyunsaturated FAs, 0.5% ALA , 12% monounsaturated FAs), which substituted the amount of ALA from walnuts in the WD with oleic acid. This design enabled evaluation of the effects of whole walnuts versus constituent components. The primary end point, central systolic blood pressure, was unchanged, and there were no significant changes in arterial stiffness. There was a treatment effect ( P=0.04) for central diastolic blood pressure; there was a greater change following the WD versus the oleic acid-replaced-ALA diet (-1.78±1.0 versus 0.15±0.7 mm Hg, P=0.04). There were no differences between the WD and the walnut fatty acid-matched diet (-0.22±0.8 mm Hg, P=0.20) or the walnut FA-matched and oleic acid-replaced-ALA diets ( P=0.74). The WD significantly lowered brachial and central mean arterial pressure. All diets lowered total cholesterol, LDL (low-density lipoprotein) cholesterol, HDL (high-density lipoprotein) cholesterol, and non- HDL cholesterol. Conclusions Cardiovascular benefits occurred with all moderate-fat, high-unsaturated-fat diets. As part of a low- SFA diet, the greater improvement in central diastolic blood pressure following the WD versus the oleic acid-replaced-ALA diet indicates benefits of walnuts as a whole-food replacement for SFA . Clinical Trial Registration URL : https://www.clinicaltrials.gov . Unique identifier: NCT02210767.

Keywords: arterial stiffness; bioactives; nutrition; polyunsaturated fatty acids; pulse‐wave velocity; walnuts; α‐linolenic acid.

Figures

Figure 1

Study design for this randomized, 3‐period, crossover, controlled‐feeding trial. ↑ indicates end point testing (vascular assessment and fasting blood draw completed on the last 2 days of the run‐in diet and study diets). The average compliance break between diet periods was 23 days. All foods and caloric beverages were provided for all diet periods and the run‐in diet.

Figure 2

CONSORT diagram of participant flow through the study. BMI indicates body mass index; BP, blood pressure; CONSORT, Consolidated Standards of Reporting Trials; LDL‐C, low‐density lipoprotein cholesterol.

Figure 3

Mean changes from baseline for blood pressure and vascular measures following each of the three 6‐week study diets (n=45). Data are presented as unadjusted mean±SEM. Change scores were calculated by subtracting the values following the run‐in diet from values following each study diet and were compared using the MIXED procedure (SAS v9.4; SAS Institute). There was a significant reduction in bMAP, cDBP, and cMAP from baseline following the WD. Post hoc comparisons showed a significant difference in cDBP between the WD compared with the ORAD and no differences between the WD and the WFMD or the WFMD and the ORAD. Post hoc pairwise tests were adjusted for multiple comparisons using the Tukey–Kramer method; statistically significant between‐diet effects are denoted with differing letters (P<0.05). AIx indicates augmentation index; AP, augmentation pressure; bDBP, brachial diastolic blood pressure; bMAP, brachial mean arterial pressure; bSBP, brachial systolic blood pressure; cDBP, central DBP; cMAP, central MAP; cSBP, central systolic BP; HR, heart rate; ORAD, oleic acid–replaces–α‐linolenic acid diet; PTT, pulse transit time; PWV, pulse‐wave velocity; WD, walnut diet; WFMD, walnut fatty acid–matched diet.

Figure 4

Mean changes from baseline for lipids and lipoproteins following each of the three 6‐week study diets (n=45). Change scores were calculated by subtracting the values following the run‐in diet from values following each study diet and were compared using the MIXED procedure (SAS v9.4; SAS Institute). There was a significant reduction in TC, LDL‐C, non–HDL‐C, and HDL‐C after all diets compared with baseline. *P<0.05 for the within‐diet change from baseline. LDL‐C indicates low‐density lipoprotein cholesterol; non–HDL‐C, non–high‐density lipoprotein cholesterol; TC, total cholesterol; TG, triglycerides.