Reference
Kay CD, Gebauer SK, West SG, Kris-Etherton PM. Pistachios increase serum antioxidants and lower serum oxidized–LDL in hypercholesterolemic adults. J Nutr. 2010;140(6):1093-1098
Design
A randomized, crossover controlled-feeding study to evaluate 2 doses of pistachios on serum antioxidants and biomarkers of oxidative status
Participants
28 hypercholesterolemic adults (LDL-cholesterol ≥2.86 mmol/L)
Study Medication and Dosage
After a 2-week baseline Western Diet, participants ate one of 3 diets, all providing similar caloric intake for 4 weeks. The control diet contained no pistachios and was lower fat (25% total fat). The two other diets contained either 1 or 2 servings of pistachios each day. A serving consisted of 32 to 63 grams of nuts.
Main Outcome Measures
Plasma lutein, alpha-carotene, beta-carotene, gamma-tocopherol, lipid profiles, and oxidized LDL
Key Findings
Both the 1-serving/day and 2-serving/day pistachio–enriched diets significantly reduced levels of oxidized LDL compared to the control diet
Practice Implications
The quantity of LDL found in the blood is a long-established marker for cardiovascular disease risk. More recently, the amount of oxidized LDL (Ox-LDL) has gained recognition as a contributing factor for the initiation and progression of cardiovascular disease.1 High levels of Ox-LDL are associated with greater risk of metabolic syndrome, coronary heart disease, and acute coronary syndrome.2 Lowering Ox-LDL, as this study tells us pistachios will do, is an important goal for disease prevention. Prior studies have already established that eating pistachios improves standard lipid profiles.
This current paper by Kay et al is in fact a further analysis of data from a clinical trial of pistachio nuts that was first published in 2008 by Gebaur et al.3 The initial analysis of the data looked specifically at the effects of a high-pistachio diet on more common cardiovascular risk factors. Blood samples and data from the same controlled feeding study were analyzed for both papers. Gebauer et al reported that those participants eating 2 doses of pistachios per day decreased total cholesterol by 8%, LDL cholesterol by 11.6% (P < 0.05) compared with the control diet. The total cholesterol/HDL cholesterol ratio and the LDL cholesterol/HDL cholesterol ratio for this group of participants dropped 8% and 11% respectively (P < 0.05).
These papers do not stand alone in suggesting that pistachios and other nuts are beneficial at reducing cardiovascular disease risk.
These papers do not stand alone in suggesting that pistachios and other nuts are beneficial at reducing cardiovascular disease risk. In April 2010, Sari et al from the Gaziantep University School of Medicine in Turkey reported on their own pistachio feeding trial. They had fed 32 healthy young men a Mediterranean diet for a month and then added pistachios for an additional month. Compared with the Mediterranean diet, the pistachio diet decreased glucose by 8.8% (±8.5%, P < 0.001), decreased LDL by 23.2% (±11.9%), decreased total cholesterol by 21.2% (±9.9%, P < 0.001), and triglycerides by 13.8% (±33.8%, P = 0.008). The pistachio diet significantly improved endothelium-dependent vasodilation by 30% (P = 0.002), decreased serum interleukin-6, total oxidant status, lipid hydroperoxide, and malondialdehyde and increased superoxide dismutase (P < 0.001 for all).4
In 2007 Sheridan et al reported on a randomized controlled crossover trial in which pistachios were fed to 15 volunteers for 4 weeks in amounts that would contribute 15% of their total calories. Statistically significant reductions were seen in total cholesterol/HDL ratios (-0.38; 95% CI, -0.57 to -0.19; P = 0.001), LDL/HDL (-0.40; 95% CI, -0.66 to -0.15; P = 0.004), and a statistically significant increase was seen in HDL (+2.3; 95% CI, 0.48 to 4.0; P = 0.02).5
Other nuts also have been shown to improve lipid panels. In May 2010, Sabaté and colleagues at California’s Loma Linda University reported on a pooled analysis of intervention trials on nuts and blood lipids.6 They pooled individual primary data from 25 nut consumption trials conducted in 7 countries among 583 men and women with normolipidemia and hypercholesterolemia who were not taking lipid-lowering medications. In the pooled data, mean nut consumption was 67 grams per day. Total cholesterol concentration decreased by 10.9 mg/dL (-5.1% change). LDL cholesterol decreased by 10.2 mg/dL (-7.4% change). The LDL/HDL ratio decreased by 0.22 (-8.3% change) and the total cholesterol/HDL ratio dropped by 0.24 (-5.6% change) (P < .001 for all). Triglyceride levels decreased by 20.6 mg/dL (-10.2%) in subjects whose levels were greater than 150 mg/dL (P < .05).
Not all the nut studies have been equally positive. Phung et al wrote a meta-analysis of 5 trials on almonds with a total of 142 participants and found a neutral effect on lipid profiles.7 A year before, Jenkins reported that almonds do decrease levels of lipid oxidation.8 So even if almonds have a neutral effect on lipid levels, they may still offer cardiovascular protection.
In addition to the results of these feeding trials, support for the cardiovascular benefits of eating nuts is accumulating from epidemiologic studies as well. Sabaté and Wien in a review published in May of 5 large epidemiologic studies report “an 8.3% reduction in risk of death from coronary heart disease for each weekly serving of nuts.”9
Given the number and strength of the studies on nuts and the number of years since these benefits were first noticed (Sabaté’s first paper on walnuts was published in 1993), it is surprising that many medical practitioners are unaware that nuts are now considered beneficial.10 Patients still inform me that their medical doctors have advised them to ‘cut back on the nuts’ in order to lower their cholesterol. This is a medical myth that we should be loudly proactive in refuting. Getting patients to increase nut consumption, to choose nuts as a snack, or to add them as an ingredient to other foods is a simple intervention that the evidence suggests will produce benefits.
