Pistachio Diet Improves Erectile Function Parameters and Serum Lipid Profiles in Patients with Erectile Dysfunction

M Aldemir; E Okulu; S Neşelioğlu; O Erel; Ö Kayıgil

Disclosures

Int J Impot Res. 2011;23(1):32-38. 

In This Article

Discussion

After a pistachio diet of 3 weeks, total IIEF scores and five domains showed a statistically significant increase (Table 3). PCDU of patients showed a statistically significant increase in the value of PSV. EDV showed an improvement but it was not statistically significant (Table 4), which may be attributed to the small number of cases.

Pistachio nuts are rich sources of some plant proteins, dietary fibers and especially antioxidant substances, besides being high in unsaturated fatty acids and saturated fatty acids (Table 1). In addition, pistachio nuts are relatively high in the nonessential amino acid arginine, which appears to maintain flexible arteries and to enhance blood flow by boosting nitric oxide, a compound that relaxes blood vessels.[17] Sari et al.[6] demonstrated that a pistachio diet resulted in an improvement in endothelium-dependent vasodilation in normolipidemic healthy young men. Improvement of blood vessel relaxation and endothelium-dependent vasodilatation might be related with significantly increased PSV values in PCDU in our study.

Oxidative stress decreased synthesis and bioavailability of endothelial and neuronal nitric oxide.[18] We know that pistachio nuts are rich sources of antioxidant substances (Table 1). Kocyigit et al.[14] reported that a 3-week pistachio diet in healthy volunteers had a favorable effect on oxidative stress. They found a decrease in malondialdehyde level and an increase in antioxidant potential. Serum interleukin-6, total oxidant status, lipid hydroperoxide and malondialdehyde levels were detected to be decreased following administration of 60–100 g pistachio diet for 4 weeks in another study.[6] The antioxidant effects of pistachio against oxidative damage might originate from phytochemicals in its content as resveratrol and anthocyanins have strong free radical scavenging ability.[14,19]

PON1 (paraoxonase 1) and arylesterase, the HDL-bound enzyme system, are well-known antioxidant molecules. This enzyme system protects LDL and HDL from oxidation by hydrolyzing activated phospholipids and lipid peroxide products, and thus prevents atherosclerosis. Additionally, PON1 activity was suggested to modulate endothelial functions.[20] Ciftci et al.[21] reported that the PON1 activity was found significantly lower in patients with ED compared with the control group.

Aksoy et al.[22] used 20 and 40% of daily caloric intake pistachio diet for 10 weeks in an experimental study in rats. Consumption of pistachio as 20% of daily caloric intake resulted in a significant improvement in HDL cholesterol and TC/HDL ratio. Moreover, consumption of pistachio as 20% of daily caloric intake increased PON1 activity by 35% and arylesterase activity by 60%, which inhibits oxidation of LDL cholesterol. They also found out that consumption of pistachio as 20% of daily caloric intake resulted in better outcomes compared with 40% of daily caloric intake.

The association between hyperlipidemia and ED is originally attributed to atherosclerosis in the hypogastric-cavernosal arterial bed, with a subsequent insufficiency in penile arterial inflow.[23] Impairment of endothelium-dependent relaxation in numerous vascular beds in men with hypercholesterolemia has been firmly established.[24–26] These impairments have also been shown to be reversible, using lipid-lowering therapies.[27] Another study related to this subject showed that the association between hyperlipidemia and ED is attributed to the impairment of endothelium-dependent relaxation in smooth muscle cells of corpus cavernosum by hypercholesterolemia.[28] Wei et al.[29] demonstrated that a high level of TC and a low level of HDL are important risk factors for ED. In this study, every mmol l–1 increase in TC was associated with a 1.32-fold increase in the risk of ED. Men with TC >240 mg dl–1 had 1.83 times the risk than did men with <180 mg dl–1.[29] Pinnock et al.[30] showed that high cholesterol level was an independent predictor of impotence. Manning et al.[31] found a correlation between high LDL and organic ED (68.6 vs 32.4% in the psychogenic impotence group), and a clear positive correlation between high LDL and cavernovenous insufficiency was determined. Nikoobakht et al.[32] demonstrated that there was a significant correlation between total cholesterol and LDL with ED. According to this study, every mg dl–1 increase in plasma cholesterol and LDL levels decreased IIEF-5 scores by 0.036 and 0.035, respectively. Improvement of serum lipid profiles might be related with increase in IIEF scores in our study.

Another study showed HDL and TC/HDL ratio as significant predictors of ED.[33] It was also stated that decreased serum lipid levels might have contributed to penile tumescence.[33] All these studies suggest a relationship between serum lipid profiles and ED. Improvement in serum lipid profiles seems to also improve erectile functions.

Previous studies about the effect of pistachio on lipid parameters have shown favorable effects.[11,14,15] Sheridan et al.[11] reported that 4 weeks of pistachio diet as 15% of daily caloric intake caused significant decreases in TC/HDL ratio (from 4.7 to 4.4) and LDL/HDL ratio (from 3.1 to 2.8) along with a significant increase in HDL (from 55 to 57 mg dl–1) in subjects with moderate hypercholesterolemia. Kocyigit et al.[14] reported that 3 weeks of pistachio diet as 20% of daily caloric intake caused significant decreases in TC levels (from 4.08±0.69 to 3.61±0.60 mmol l–1) and TC/HDL (from 3.98±1.41 to 3.17±1.04) and LDL/HDL (from 1.82±0.51 to 1.58±0.47) ratios, and a significant increase in HDL (from 1.01±0.28 to 1.28±0.27 mmol l–1) in normolipidemic healthy volunteers. TG and LDL levels were found to be unchanged.[14] Edwards et al.[15] demonstrated that 3 weeks of pistachio diet as 20% of daily caloric intake caused significant decreases in TC (from 243 to 239 mg dl–1), TC/HDL ratio (from 4.8 to 4.5) and LDL/HDL ratio (from 3.2 to 3.1), and a significant increase in HDL (from 50 to 56 mg dl–1) in moderately hypercholesterolemic patients, whereas TG and LDL levels remained unchanged.

In our study, we observed a significant decrease in TC (from 179.5 to 148.3 mg dl–1) levels, LDL (from 106.1 to 84.8 mg dl–1) and TC/HDL (from 4.3 to 2.4) and LDL/HDL (from 2.6±to 1.4) ratios, and an increase in HDL (from 42 to 62.1 mg dl–1) levels among pistachio nuts consumers. Although statistically not significant, a decrease in TG levels was found. In addition, TG/HDL ratio (from 4 to 2.1) was significantly decreased (Table 5). To the best of our knowledge, our study is the first that demonstrated that pistachio nuts decreases serum TG/HDL ratio.

Similar to the previous studies, we used pistachio diet for 3-week duration. However, in our study, patients only consumed the pistachio diet during lunch, in order to provide maximum absorption. This was different than the other studies. More than 50% of our patients were normolipidemic and rest of them was hyperlipidemic (Table 2). Following 3-week pistachio diet, improvement in lipid profiles was detected in all patients.

Several hypotheses have been suggested for the serum lipid-lowering effect of pistachio nuts. Pistachio nuts are generally low in saturated fatty acids and high in unsaturated fatty acids. Unsaturated fatty acids (both monounsaturated and polyunsaturated) have been shown to reduce serum TC and LDL. In addition, pistachio nuts contain significant amounts of phytosterols. The major phytosterol component is β-sitosterol, which is one of several plant sterols implicated in cholesterol lowering.[34]

Edwards et al.[15] showed that the decrease in cholesterol could be attributed to the intake of high soluble fiber and phytosterols. Soluble fibers and other plant proteins, such as soy proteins found in pistachio nuts, also increase the level of HDL cholesterol.[35] Arginine may account for the hypocholesterolemic effect observed in animal studies.[36]

In our study, significant decrease in serum testosterone levels was detected in patients who had pistachio diet (from 452.1 to 379.1 ng dl–1). Pistachios are known to have phytosterol. Animal models show that a high intake of phytosterols will reduce serum testosterone levels.[37]

Platelets have been suggested to have a role in the pathogenesis of ED. Particularly in vasculogenic ED, platelets were suggested to stick to the cavernosal walls and secrete mediators, leading to an increase in oxidative stress during erection.[38] In our study, significant decrease in blood platelet counts were detected following pistachio diet (from 305.6 to 242.4). To the best of our knowledge, this particular effect of pistachio nuts is demonstrated only in our study. Decrease in platelet count might lead to improved blood flow and improvement in PCDU parameters.

As pistachio nuts are fatty food, the consumers may have concerns about gaining weight. However, in our study, we observed that body mass index did not show a change before or after the pistachio diet. Similar to our study, previous studies demonstrated that people who consume up to 20% of the daily calorie intake did not show an increase in body mass index and weight gain.[6,14]

Conclusions

We have shown that 3-week pistachio diet applied to patients with ED resulted in a significant improvement in erectile function parameters (PCDU parameters and IIEF scores) with additional improvement in serum lipid parameters without any side effects. Further studies are needed with increased number of patients and longer follow-up evaluating the relationship between pistachio nuts and ED pathogenesis.

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