Abstract
Studies showed that nut consumption is associated with a reduced risk in cardiovascular disease (CVD) mortality and morbidity and an improvement in the modifiable CVD risk factors. Our objective was to review studies that reported the effect of pistachios intake on blood lipid profile. A PUBMED and Loma Linda University Nut Library database search was conducted to identify relevant studies. Eight relevant studies were identified and included in the review. With a few exceptions, the results showed a consistent improvement in serum lipid profile, improving all cholesterol fractions. With one exception, all studies reported a large decrease in the mean LDL-cholesterol ranging from 7.6 to 9.7% of the baseline level. In four of the seven studies that reported a change in HDL-cholesterol level, the mean HDL-cholesterol increased after the intervention. In all but one studies that reported the change in TG, the post-test values were reduced. The majority of the studies reported statistically significant reduction in the mean TC and LDL-cholesterol fractions. Similarly, all studies that reported a change in TC/HDL-cholesterol and LDL-cholesterol/HDL-cholesterol ratios reported a statistically significant improvement. Adding pistachios to a typical diet of normo and hypercholesterolemic individuals have a beneficial effect on blood lipid profile.
Keywords
Pistachios are rich in protein, monounsaturated fatty acids (MUFAs), and polyunsaturated fatty acids (PUFAs).
Introduction
In 1991, Frazer et al 1 published the first study showing a possible reduced risk of coronary heart disease (CHD) related to frequent nut intake. Since then, close to 300 manuscripts have been published reporting a beneficial impact of nut consumption on various cardiovascular diseases (CVDs) and CVD risk factors. Such beneficial effect is believed to be a result of the nutritional profile of nuts. 2
Pistachios have one of the most beneficial nutrient content of any nuts. Pistachios are rich in protein, monounsaturated fatty acids (MUFAs), and polyunsaturated fatty acids (PUFAs). They are also relatively low in saturated fatty acids (SFAs) and contain no transfatty acids or cholesterol. In addition, unlike most other nuts, except for peanuts, pistachios also contain resveratrol, a compound associated with reduced risk of CVD and a few other chronic health conditions.3,4 They also contain other beneficial compounds, such as phytochemicals, associated with reduced risk for CVD. 2 The nutritional profile of pistachios is listed in Table 1.
Nutritional Profile of Pistachios. a
US Department of Agriculture National Nutrient Database for Standard Reference. 12
Most research that assessed the association between nuts and CVD has focused on total nut intake, walnuts alone, or almonds alone. The limited research with pistachios indicates that adding pistachios to a diet may result in an improvement of blood lipid profile and other risk factors for CVD, including lower body weight, enhanced endothelial function, reduced inflammation, and improved serum glucose control.5-11 The goal of this review was to evaluate the effect of pistachio intake on blood lipid profile.
Methods
A PubMed and Loma Linda University Nut Library (LLUNL) database search was conducted to identify relevant studies. The goal of the search was to identify articles that assessed blood lipid change using pistachios alone. Using pistachio as a word in a title, a PubMed search yielded 108 and LLUNL 15 matches. After screening the titles and abstracts, 7 articles were identified and included in the review.5-11
Results
A controlled, randomized crossover study conducted by Edwards and colleagues 5 evaluated the impact of substituting pistachios for 20% of daily caloric intake from high-fat snacks or in place of fat calories on serum lipid profile. The sample consisted of 10 moderately hypercholesterolemic individuals, 4 men (age range = 41-53 years) and 6 women (age range = 28-64 years). One-half of the participants consumed a pistachio-containing diet, whereas the other half consumed a regular diet. After 3 weeks of dietary modifications, a reduction in the mean total cholesterol (TC) from 243 to 239 mg/dL (P < .04), a decrease in the mean low-density lipoprotein (LDL) cholesterol from 180 to 158 mg/dL (not statistically significant), and an increase in the mean high-densitylipoprotein (HDL) cholesterol from 50 to 56 mg/dL (P < .09) was observed. In addition, triglycerides (TG) decreased from 113 to 108 mg/dL (not statistically significant), the ratio of TC to HDL cholesterol decreased from 4.8 to 4.5 (P < .01), and the ratio of LDL cholesterol to HDL cholesterol decreased from 3.2 to 3.1 (P < .02). 5
Gebauer and colleagues 6 conducted a study on the effects of pistachio consumption on cholesterol levels in 10 men and 18 women, with a mean age of 51 years. Participants consumed a control diet (low-fat diet with no pistachios), or 1 serving of pistachios-containing diet, or 2 servings of pistachios-containing diet. The mean TC decreased from 5.40 to 5.01 mmol/L (P < .05) for those on the 1 serving of pistachios diet and to 4.92 mmol/L (P < .05) for those on the 2 servings of pistachios diet. Similarly, the mean LDL cholesterol decreased from 3.43 to 3.08 mmol/L (P < .05) and to 2.98 mmol/L (P < .05) on the 1- and 2-serving diets, respectively. In contrast, the HDL cholesterol changed on the 1-serving diet from 1.48 to 1.43 mmol/L and was raised back to 1.48 mmol/L on the 2-serving diet. The mean TG increased from 1.15 at baseline to 1.28 mmol/L (P < .05) and 1.20 mmol/L (P < .05) on the 1- and 2-serving diets, respectively. The TC to HDL cholesterol ratio decreased from 3.85 to 3.78 (P < .05) and to 3.50 (P < .05) on the 1- and 2-serving diets, respectively. The same was true of the LDL to HDL cholesterol ratio—a change from 2.48 at baseline to 2.38 (P < .05) and 2.15 (P < .05) on the 1- and 2-serving diets, respectively. 6
Aldemir and colleagues 7 reported a change in blood lipid levels among patients with erectile dysfunction. For 3 weeks, 17 married men, mean age (standard deviation [SD]) = 47.9 (6.2) years, consumed a 100-g pistachios-containing diet. A decrease in the mean TC from 179.5 to 148.3 mg/dL (P < .008), LDL cholesterol from 106.1 to 84.8 mg/dL (P < .007), and TG from 160.8 to 133.9 mg/dL (P < .288) was observed. The mean HDL cholesterol on the other hand increased from 42 mg/dL to 62.1 mg/dL (P < .001). A significant decrease in TC to HDL cholesterol ratio from 4.3 to 2.4 (P < .001) and LDL to HDL cholesterol ratio from 2.6 to 1.4 (P < .001) was also seen. 7
Sheridan et al 8 conducted a randomized crossover study to determine the effects of pistachios on serum lipid profile when 15% of daily caloric intake was substituted with pistachios for high-fat snacks. A total of 15 moderately hypercholesterolemic participants (11 men and 4 women), mean age 60 years, consumed a pistachio-containing diet for 4 weeks. The mean TC decreased from 246 to 237 mg/dL (P < .11), mean LDL cholesterol level also decreased from 164 to 148 mg/dL (P < .06), and the mean HDL cholesterol increased from 55 to 57 mg/dL (P < .02). The mean TG level was reduced from 141 to 131 mg/dL (P < .11).Both TC to HDL cholesterol ratio and LDL to HDL cholesterol ratios also decreased from 4.7 to 4.4 (0.01) and from 3.1 to 2.8 (0.009), respectively. Furthermore, the apolipoprotein (apo) B-100 decreased from 132 to 119 mg/dL (P < .11), whereas apo A1 increased from 135 to 146 mg/dL (P < .17). Similarly, the B-100 to apo A1 ratio decreased from 1 to 0.83 (P = .009). 8
Sari et al 9 conducted a study with 32 students, age range = 21 to 24 years, in a police school in Turkey. Students received a Mediterranean-type of a diet for 4 weeks and, then, a similar diet in which 20% of calories from MFAs were replaced by pistachios. After 4 weeks, the mean TC reduced from 190.7 to 149.4 mg/dL (P < .001). Similarly, the mean LDL cholesterol decreased from 124.5 to 95 mg/dL (P < .001), and the mean TG level changed from 112.1 to 91.1 mg/dL (P < .0008). The mean HDL cholesterol also changed from 43.5 to 41.7 mg/dL (P < .069). The cholesterol ratios were also reduced from 4.40 to 3.78 (P < .001) in the case of TC to HDL cholesterol ratio and from 2.88 to 2.30 (P < .001) for LDL to HDL cholesterol ratio. The mean lipoprotein apo A1 level was reduced from 1.34 to 1.20 (P < .001) and apo B from 0.64 to 0.57 (P < .001). Similarly, the mean apo B to apo A1 ratio decreased from 0.49 to 0.48 (P < .1). 9
Kocyigit et al 10 investigated whether pistachio consumption affected the plasma lipid profile and oxidative status in 44 healthy volunteers (24 men and 20 women) with normal lipid levels. One-half of the participants, mean (SD) age = 32.8 (6.7) years, were randomly assigned to a regular diet group and the other half, mean (SD) age = 33.4 ± 7.2 years, to a pistachio-containing diet group (20% of daily caloric intake, 65-75 g/d) for 3 weeks. A significant decrease was observed from baseline in the pistachios-containing diet group in the mean plasma TC from 4.08 to 3.61 (0.6) mmol/L (P < .05) and LDL cholesterol from 1.94 to 1.89 mmol/L (P < .05), and an increase was seen in the mean HDL cholesterol from 1.01 to 1.28 mmol/L (P < .27). The mean TG level decreased from 1.34 to 1.18 mmol/L (P < .05). Decreases in both TC to HDL cholesterol and LDL to HDL cholesterol ratios were also detected, from 3.98 to 3.17 (P < .01) and from 1.82 to 1.58 (P < .001),respectively. 10
Li et al 11 assessed the effect of pistachio snack consumption on body weight and serum lipids in 59 individuals, age range = 20 to 65 years. In all, 31 of these individuals consumed a 500-kcal deficit diet to which a snack with 53 g of salted pistachios was added; the remaining 28 people consumed a 500-kcal deficit diet with a snack composed of 56 g of salted pretzels for 12 weeks. In the pistachios group, TC decreased from a mean of 197.4 at baseline to 191.4 mg/dL at 6 weeks and 191.6 mg/dL at 12 weeks. The mean LDL cholesterol was basically unchanged at 6 weeks (83.1 vs 83.4 mg/dL) and decreased slightly to 79.9 mg/dL at 12 weeks. The mean HDL cholesterol value was 43.8 mg/dL at baseline, 40.3 mg/dL at 6 weeks, and 42.9 mg/dL at 12 weeks. The mean TG level decreased considerably from 113 mg/dL at baseline to 88.0 mg/dL at 6 weeks, and 88.1 at 12 weeks. Only the change in TG level was statistically significant at P < .05. 11
Discussion
Studies have shown that individuals who consume nuts frequently have lower risk for CVD, indicating that nuts may play an important role in CVD prevention. 1 Studies that focused on CVD biomarkers and risk factors, such as serum lipid profile, body weight, oxidation, blood glucose, endothelial function, and inflammation, showed that nuts, including pistachios, positively affect all of the above.5-11 The results of this review confirm the beneficial effect of pistachios on blood lipid profile.
Studies included in this review were based on relatively small sample sizes, ranging from 10 to 59 participants. Of these studies, 3 evaluated the effect of pistachios in hypercholesterolemic and 4 in normocholesterolemic individuals. The study period varied from 3 to 12 weeks, and the amount of pistachios consumed ranged from 1 to 2 servings or 15% to 20% of calories consumed. The results also varied greatly from almost no change in TC in the study by Edwards et al 5 with hypercholesterolemic individuals (−4 mg/dL, after 3 weeks) to about 40 mg/dL reduction in a study conducted by Sari et al 9 (−41.3 mg/dL, after 4 weeks) on individuals who were normocholesterolemic prior to intervention. With 1 exception, 11 in all studies, a large decrease in the mean LDL cholesterol was reported ranging from 7.6% to 9.7% of the initial level. In 4 of the 7 studies that reported a change in HDL cholesterol levels, the mean HDL cholesterol increased after the intervention.5,7,8,10 In all, but one, 6 studies that reported the change in TG, the posttest value was reduced. The majority of the studies reported statistically significant reduction in the mean TC and LDL cholesterol fractions. Similarly, all studies that reported a change in TC to HDL cholesterol and LDL to HDL cholesterol ratios reported a statistically significant improvement. These findings indicate that adding pistachios to a typical diet of normocholesterolemic and hypercholesterolemic individuals has a beneficial effect on the blood lipid profile.
Several factors are likely responsible for the improvement in blood lipid profile reported in these studies, including the replacement of SFA with PUFA and MUFA, dietary fiber, and phytosterols.3,7 Phytosterols play a significant role in lowering cholesterol levels by interfering with cholesterol absorption when sufficient amounts are in the intestinal lumen. Soluble fiber found in pistachios can prevent reabsorption of bile acids causing the liver to use circulating cholesterol for de novo bile acid synthesis.
Pistachios may protect individuals from developing heart disease in ways other than by improving serum lipids. They contain more lutein and β-carotene than other tree nuts and are high in phenol and flavonoid content. 12 Pistachios are also the only tree nut to contain resveratrol.13,14 Research has revealed a decrease in oxidation and increase in antioxidant biomarkers when pistachio-containing diets are consumed.9,10,15 For example, studies have found an increase antioxidant biomarkers, such as superoxide dismutase, and a decrease in oxidation factors, such as lipid hydroperoxide.10,11 Pistachios contain phenolic compounds, which have been shown to have powerful antioxidant effects and decrease lipid peroxidation or oxidative DNA damage.2,16
Endothelial dysfunction is associated with early and advanced atherosclerosis,which can predict future development of CHD. Endothelial dysfunction reduces nitric oxide production, essential in endothelial elasticity.2,9 Pistachios are a good source of protein and an amino acid,
The studies reviewed are subject to some limitations. All the studies included a relatively small sample size and were conducted over a small duration of time. Larger controlled-feeding studies are necessary for this type of research, to ensure accuracy. Future studies will need to be conducted, especially to assess the amount and frequency of pistachio intake that yield the most protective improvement in serum lipids.
Conclusion
The findings of this review highlight the beneficial impact of pistachio-containing diets on the serum lipid profile.5-11 Because of the beneficial impact of pistachios on serum lipid level as well as possible additional benefits highlighted above, pistachios should be considered heart healthy and should be recommended for individuals at risk for or with heart disease.