In their investigation of thirteen studies, the researchers demonstrated that walnut-rich consumption decreased total and low-density lipoprotein (LDL) cholesterol during short term trials.
However the scientists suggested that "larger and longer-term trials" are needed to observe the effects of eating walnuts, rich in polyunsaturated fatty acids, on cardiovascular risk and weight management.
Their analysis joins a blossoming body of science that has linked nut consumption – including almonds and macadamias – to improvements in markers of cardiovascular health.
Coronary heart disease places a significant financial burden on all European states, and in the UK alone costs the health system more than €5bn per year. Governments, scientists and the food industry itself continue to invest time and money in pinpointing potential dietary solutions that could boost cardiovascular health.
Design of the meta-analysis
Published in a recent issue of the American Journal of Clinical Nutrition, researchers Deirdre Banel and Frank Hu conducted the meta-analysis to, "estimate the effect of walnuts on blood lipids".
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 of lipid outcomes," said the scientists.
The 13 studies selected represented some 365 participants, with diets lasting between four and 24 weeks and walnuts providing between 10 and 24 per cent 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," the Harvard researchers wrote.
Further, the meta-analysis results gave a nod to the widening circle of potential health benefits contained in walnuts.
"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," stated the researchers.
Source: American Journal of Clinical Nutrition
May 2009, Volume 90, Pages 56-63, doi:10.3945/ajcn.2009.27457
‘Effects of walnut consumption on blood lipids and other cardiovascular risk factors: a meta-analysis and systematic review’
Authors: Deirdre K Banel and Frank B Hu