(09-07-09) Effects of walnut consumption on blood lipids and other cardiovascular risk factors: a meta-analysis and systematic review1,2,3

Deirdre K Banel and Frank B Hu

1 From the Departments of Nutrition and Epidemiology, Harvard School of Public Health, Harvard University, Cambridge, MA (DKB and FBH).
2 Supported by NIH grant HL60712 and an unrestricted educational grant from the California Walnut Commission.
3 Address correspondence to DK Banel, 665 Huntington Avenue, Boston, MA 02115. E-mail: [email protected] .
Background: Consumption of nuts has been associated with a decreased risk of cardiovascular disease events and death. Walnuts in particular have a unique profile: they are rich in polyunsaturated fatty acids, which may improve blood lipids and other cardiovascular disease risk factors.
Objectives: We aimed to conduct a literature review and a meta-analysis to combine the results from several trials and to estimate the effect of walnuts on blood lipids.
Design: Literature databases were searched for published trials that compared a specifically walnut-enhanced diet with a control diet. We conducted a random-effects meta-analysis of weighted mean differences (WMDs) of lipid outcomes.
Results: Thirteen studies representing 365 participants were included in the analysis. Diets lasted 4?24 wk with walnuts providing 10?24% of total calories. When compared with control diets, diets supplemented with walnuts resulted in a significantly greater decrease in total cholesterol and in LDL-cholesterol concentrations (total cholesterol: WMD = ?10.3 mg/dL, P < 0.001; LDL cholesterol: WMD = ?9.2 mg/dL, P < 0.001). HDL cholesterol and triglycerides were not significantly affected by walnut diets more than with control diets (HDL cholesterol: WMD = ?0.2, P = 0.8; triglycerides: WMD = ?3.9, P = 0.3). Other results reported in the trials indicated that walnuts provided significant benefits for certain antioxidant capacity and inflammatory markers and had no adverse effects on body weight [body mass index (kg/m2): WMD = ?0.4, P = 0.5; weight (kg): WMD = ?0.05, P = 0.97].
Conclusions: Overall, high-walnut-enriched diets significantly decreased total and LDL cholesterol for the duration of the short-term trials. Larger and longer-term trials are needed to address the effects of walnut consumption on cardiovascular risk and body weight.

Source: Am J Clin Nutr 90: 56-63, 2009

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