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 to 24 weeks with walnuts providing 10% to 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 [“bad”] cholesterol: WMD = –9.2 mg/dL, P < 0.001.
HDL [“good”] 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: American Journal of Clinical Nutrition, Jul 2009;90(1);56-63. PMID: 19458020, by Banel DK, Hu FB. Departments of Nutrition and Epidemiology, Harvard School of Public Health, Harvard University, Cambridge, Massachusetts, USA. [E-mail: firstname.lastname@example.org]