• Research Review
• Journal Review

Authors: J Sabate, K Oda, E Ros

Reference: Arch Intern Med 2010; 170:821-827
http://archinte.ama-assn.org/cgi/content/short/170/9/821

Reviewer: Robert Goldberg, PhD, Contributing editor, ProCor; Professor of Medicine and Epidemiology, Division of Cardiovascular Medicine, University of Massachusetts Medical School, Worcester, Massachusetts, USA

Reviewer comments: Elevated serum lipid levels have been consistently shown to be an important risk factor in the development of coronary heart disease (CHD) and other major vascular disorders. While statin therapy has been shown to be very effective in reducing one's serum lipid levels, nonpharmacologic, primarily dietary, therapeutic approaches are continually being assessed for their potentially beneficial effects on serum lipid levels, other physiologic variables, and on the different clinical manifestations of underlying coronary atherosclerosis. While a number of observational epidemiologic studies have shown an association between the consumption of nuts and a lower risk for CHD, the results of this pooled analysis of randomized clinical trials (RCTs) suggest that increased consumption of nuts, most commonly walnuts and almonds, can result in reduced serum lipid levels, particularly total cholesterol and HDL-C.

Based on the data presently available from both observational studies and RCTs, increased dietary intake of nuts that are palatable and appealing to a person appear to have beneficial effects on serum lipid levels. These data, coupled with the results of prior studies that have shown beneficial effects of nut consumption on endothelial function, oxidative stress, and other lipoprotein fractions, suggest that the regular daily consumption of a moderate amount of nuts can be of considerable benefit in the prevention of CHD.

Purpose of study: To examine the association between consumption of different types of nuts and serum lipid levels.

Location of study: Global

Study design: Meta analysis of the published literature.

Results: The authors reviewed the published literature between 1992 and 2004 for articles that assessed the effects of nut consumption on blood lipid levels. This systematic search of the literature identified 25 articles that examined this association through use of a RCT design format. These trials were carried out in seven countries and the sample sizes ranged from 10 to 49 subjects in each of these investigations. The mean age of the study sample in these pooled investigations was 46 years and a total of 583 men and women were included in these trials. In nine of the RCTs, individuals with hypercholesterolemia were included whereas 16 studies included persons with normal serum cholesterol levels. The daily nut consumption in these trials ranged from 0.8 to 4.8 ounces (average = 2.4 ounces/day) and the effects of different legumes including walnuts, almonds, pecans, macadamia nuts, and pistachios were assessed in these trials.

In comparison with the control diets, individuals who consumed the various nuts under consideration had lower total and LDL cholesterol levels, and in the ratio of either LDL or total cholesterol levels to HDL levels. The average decline in total cholesterol associated with nut consumption was 11 mg/dl, 10 mg/dl in LDL-cholesterol, and little to no change in HDL-cholesterol levels. The positive effects on blood lipid levels were seen for both men and women across all age groups, and were relatively similar for the specific type of nut consumed. Moreover, the estimated effects of nut consumption on blood lipid levels were dose related. For example, when approximately one fifth of dietary energy was obtained from nuts, average blood lipid levels for both total cholesterol and LDL-cholesterol were reduced by 10 mg/dl (approximate 5% decline); when approximately 10% of dietary energy was obtained from nuts, blood lipid levels of total cholesterol and LDL-cholesterol were reduced by approximately 6 mg/dl or 3%.