Crossover study of diets enriched with virgin olive oil, walnuts or almonds. Effects on lipids and other cardiovascular risk markers☆
Introduction
Dietary habits are potent factors influencing coronary heart disease (CHD) risk at a global level [1]. Consistent evidence from epidemiological studies suggests that the dietary pattern known as Mediterranean diet might be particularly beneficial in CHD prevention [2], [3]. Among components of the Mediterranean diet, the frequent intake of two foods that are rich in unsaturated fatty acids and other bioactive nutrients, olive oil [4] and nuts [5], [6], has shown a beneficial impact on intermediate markers of cardiovascular risk. Nut consumption has also been associated with reduced CHD outcomes in prospective studies [7].
Early results from the PREDIMED study, a clinical trial in persons at high cardiovascular risk testing two Mediterranean diets, enriched with either virgin olive oil (VOO) or mixed nuts, versus a low-fat control diet for outcomes on cardiovascular disease events, showed both LDL-cholesterol lowering and HDL-cholesterol raising effects of the two Mediterranean diets after intervention for 3 months in 772 participants [8]. In this study there were no among-group differences in consumption of saturated fatty acids, cholesterol or fiber, suggesting that the supplemental foods (VOO and nuts) were influential in the LDL-cholesterol response. Many clinical trials using different types of nuts have consistently reported a cholesterol lowering effect of nut-enriched diets when compared to similar diets without nuts [5], while the few studies that have tested VOO (rich in polyphenols) versus oils with a lower phenolic content but with similar monounsaturated fatty acid (MUFA) composition have reported both an HDL-cholesterol rise and improved oxidative status, but no LDL-cholesterol changes [4], [9].
Walnuts and almonds, the two nut types most frequently studied for effects on intermediate markers of cardiovascular risk [5], [6], are also part of the PREDIMED intervention [8]. These nuts differ in fatty acid and micronutrient composition. Walnuts have a high content in polyunsaturated fatty acids (PUFAs), particularly linoleic acid and α-linolenic acid, the vegetable n−3 fatty acid, while almonds are rich in MUFA [10]. Whereas both nut types contain sizable amounts of phenolic compounds, walnuts are particularly rich in γ-tocopherol, while almonds contain abundant α-tocopherol and are richer in phytosterols [11]. An earlier study that compared walnut and almond diets for lipid outcomes found similar LDL-cholesterol responses [12]. However, the differential effects of these two nut types on markers of oxidation, inflammation and vascular reactivity have not been directly compared [6].
We report here the results of a crossover study in which a direct comparison was made among VOO, walnuts and almonds to assess their effects on serum lipids and other intermediate markers of cardiovascular risk.
Section snippets
Study subjects
Asymptomatic men and women with moderate hypercholesterolemia attending the Lipid Clinic at Hospital Clínic, Barcelona, Spain were recruited into a protocol approved by the institutional review board and gave informed consent. Eligibility criteria were age 25–75 years (after menopause in women), serum LDL-cholesterol ≥3.36 mmol/L (130 mg/dL), triglycerides ≤2.82 mmol/L (300 mg/dL), absence of chronic illnesses or secondary hypercholesterolemia, and no known allergy to nuts. None of the
Subjects and diets
We recruited 26 eligible subjects to account for possible losses before completion of the trial. In fact, only 18 participants completed the trial. Six subjects chose not to participate prior to randomization for personal reasons, mainly problems with clinic appointments. After randomization, two participants completed one and two diet sequences, respectively, but left the study because they felt it was too demanding. The clinical characteristics of these subjects did not differ from those of
Discussion
In this 12-week crossover feeding trial in 18 free-living men and women with moderate hypercholesterolemia we compared the effects of replacing 40% of the fat (22% of energy) in a healthy background Mediterranean diet with VOO, walnuts or almonds. The three test diets were associated with reductions in total cholesterol and LDL-cholesterol, with no change in HDL-cholesterol, thus improving the LDL/HDL ratio. While cholesterol lowering in response to dietary enrichment with walnuts and almonds
Role of the funding sources
The International Nut and Dried Fruit Council (INC), Reus, Spain provided funding and the supplemental foods tested. Research grants were also obtained from national and local nonprofit agencies. The funding sources were not involved in the design of the study and had no role in the collection, analysis, or interpretation of the data or in the decision to submit the manuscript for publication.
Author’s contributions
JS-S and ER designed the study and obtained funding. AP-H and MS delivered the intervention and estimated food and nutrient intake. MC and AS-V performed laboratory determinations. NRTD, MC, and ER analyzed and interpreted the data. NRTD and ER drafted the article. All authors critically reviewed the article for important intellectual content and approved the final version.
Conflict of interest
JS-S has received research funding from and is a non paid member of the International Nut and Dried Fruit Foundation, Reus, Spain. ER has received research funding from the California Walnut Commission, Sacramento, CA and is a non paid member of its Scientific Advisory Committee. All other authors have no other conflicts of interest to declare.
Acknowledgements
We thank the participants in the study for their enthusiastic collaboration and Emili Corbella for providing expert statistical assistance. CIBERobn is an initiative of ISCIII, Spain.
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Sources of funding: This study was supported in part by grants from the International Nut and Dried Fruit Council, Reus, Spain; the Spanish Ministry of Health FIS PS09/01292; and Fundació Privada Catalana de Nutrició i Lípids, Spain. AS-V is supported by post-doctoral contract FIS CD07/0083.