Elsevier

Clinical Nutrition

Volume 29, Issue 3, June 2010, Pages 373-380
Clinical Nutrition

Original Article
Effect of nut consumption on oxidative stress and the endothelial function in metabolic syndrome

https://doi.org/10.1016/j.clnu.2009.12.008Get rights and content

Summary

Background & aims

Oxidative stress has a key role in atherosclerosis, cancer and other chronic diseases. Some bioactive compounds in nuts have been implicated in antioxidant activities.

Objective

We assessed how nut consumption affected several markers of oxidation and endothelial function (EF) in metabolic syndrome (MetS) patients.

Patients and methods

A randomized, controlled, parallel feeding trial was conducted on 50 MetS adults who were recommended a healthy diet supplemented or not with 30 g of mixed nuts (Nut and Control groups, respectively) every day for 12 weeks. The plasma antioxidant capacity (AC), oxidized LDL (oxLDL), conjugated diene (CD) formation, urine 8-isoprostanes, DNA damage assessed by yield of urine 8-oxo-7,8-dihydro-2′-deoxyguanosine (8-oxo-dG), and EF assessed by peripheral artery tonometry (PAT) and biochemical markers, were measured at baseline and the end of the intervention.

Results

No significant differences in changes between groups were observed in AC, oxLDL, CD, 8-isoprostanes or EF during the intervention, whereas the reduction in DNA damage was significant in the Nut group compared to Control group (P < 0.001).

Conclusion

Nut consumption has no deleterious effect on lipid oxidation. The decrease in DNA damage observed in this study could contribute to explain the beneficial effects of regular nut consumption on some MetS features and several chronic diseases.

Introduction

Epidemiological studies have consistently demonstrated that frequent nut consumption is associated with reduced risk of developing coronary heart disease (CHD), type 2 diabetes, or death by overall mortality causes.1 It has been claimed that the favourable effects of nuts on the plasma lipoprotein profile is the main mechanism that explains the marked reduced risk of CHD observed in cohort studies.2 However, it has been suggested that other mechanisms of action, such as decreasing inflammation or improving EF, are important for explaining the beneficial effect of nuts on cardiovascular health.

Because of their increasingly recognized healthy benefits, nuts are currently included in several dietary guidelines worldwide and have been proposed as a component of optimal diets for CHD prevention.3, 4

However, nuts are fatty foods and presumably for this reason, until recently, were ignored or treated with a great deal of caution on most dietary recommendations. One of the possible deleterious effects of chronic nut consumption may be because nuts, especially walnuts, very rich in polyunsaturated fatty acids (PUFA).5 Of the various fatty acids, PUFA are the most susceptible to oxidation.6 In fact, a diet enriched with linoleic acid increases LDL oxidation in both human7 and animal experiments.8 This is important because current evidence indicates that oxidative damage plays a key role in atherosclerosis, cancer and other chronic diseases.9

However, emerging evidence indicates that some bioactive compounds in nuts probably counteract the pro-oxidant effect of PUFA on LDL10, 11, 12 and have elicited some cardioprotective effects.6 Several phytochemicals that have been shown to be common in nuts—e.g. polyphenols and phytoesterols—have a variety of bioactions that have been implicated in antioxidant activities. These phytochemicals may work in synergy with other important nut constituents such as antioxidant vitamins (α-tocopherol, γ-tocopherol) and minerals that decrease the oxidative damage to lipids, proteins, and lipoproteins and slow down the progression of the atherosclerosis plaque.13

However, the effect of nut consumption on oxidation has not been well studied. In fact, the effect of nut consumption on oxidative stress has been analyzed in only a few clinical trials, and only in eight was the main outcome related to oxidation. These studies have been conducted in different populations, using different types of nuts, and oxidative damage has been explored using different techniques and approaches, which explains the contradictory results obtained.14 The effect of nut consumption on EF has also been poorly studied and the results are contradictory.12, 15

Therefore, the aim of our study is to evaluate the effect of nut consumption on several steps of the cascade oxidation and endothelial dysfunction in a non diabetic MetS population. The lipid profile, the insulin resistance and the inflammatory responses from this feeding trial have been previously described.16

Section snippets

Subjects

Sixty-one male and female volunteers, aged between 18 and 65 y old with MetS from three Primary Care Centres (Alcover, Riudoms and Reus) of our zone and the University Hospital Sant Joan, Reus (Spain) were screened. To be enrolled the subjects had to have at least three of the following MetS components as defined by the updated Adult Treatment Panel (ATP III) criteria: (a) waist circumference ≥102 cm for men and ≥88 cm for women, (b) triglycerides (TG) ≥1.7 mmol/L or drug treatment for elevated

Results

A total of 61 subjects were assessed for inclusion in the study. Of these, 4 did not meet the inclusion criteria, 4 had severe difficulties in following the study and 1 had started statine therapy just before the randomization. Of the 52 participants randomized, 2 withdrew from the study for personal reasons. A total of 50 subjects (25 in the Control group and 25 in the Nut group) completed the trial and were included in the statistical analyses (Fig. 1). The average age of the 28 men and 22

Discussion

The results of our feeding clinical trial show that, despite the adverse pro-oxidant effect of consuming PUFA in nuts, especially high in walnuts, the consumption of a supplement of 30 g of mixed nuts (walnuts, almonds and hazelnuts) in a context of a healthy diet for 12 wk did not produce a deleterious effect on oxidative stress biomarkers or the endothelial function in MetS patients compared with patients consuming the same healthy diet without nuts. Moreover, DNA damage (measured by the

Conflict of Interest

J. Salas-Salvadó has received research funding from the International Nut Council, Reus, Spain. He is a nonpaid member of the Scientific Advisory Board of the International Nut Council. Mònica Bulló, Patricia Casas-Agustench, Patricia López-Uriarte, Lluís Masana, Rosa Nogués, Marta Romeu, Guillermo Saez and Carmen Tormos, no conflict of interest.

Contribution authors

PLU and JSS wrote the paper; JSS and MB designed the research and had primary responsibility for final content; PLU and PCA conducted research and analyzed data; PLU, PCA, MB, RN, MR, GS and CT conducted experiments of the research. MB, LM, GS, critically reviewed the paper. All authors read and approved the final manuscript.

Acknowledgements

This study was supported by the Spanish Ministry of Education and Science (CICYT-AGL2005-0365), Spanish Ministry of Health (RTIC RD06/0045), and the International Nut Council. Borges S.A. (Reus, Spain) donated the walnuts used in this study. CIBER Fisiopatología de la Obesidad y Nutrición (CIBEROBN) is an initiative of ISCIII. Patricia López-Uriarte is the recipient of a predoctoral fellowship from the Generalitat de Catalunya's Department of Universities, Research and the Information Society

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