Abstract

PurposeOlive pomace is a major waste product of olive oil production but remains rich in polyphenols and fibres. We measured the potential of an olive pomace-enriched biscuit formulation delivering 17.1 ± 4.01 mg/100 g of hydroxytyrosol and its derivatives, to modulate the composition and metabolic activity of the human gut microbiota.MethodsIn a double-blind, controlled parallel dietary intervention 62 otherwise healthy hypercholesterolemic (total plasma cholesterol 180–240 mg/dl) subjects were randomly assigned to eat 90 g of olive pomace-enriched biscuit (olive-enriched product, OEP) or an isoenergetic control (CTRL) for 8 weeks. Fasted blood samples, 24-h urine and faecal samples were collected before and after dietary intervention for measurement of microbiota, metabolites and clinical parameters.ResultsConsumption of OEP biscuits did not impact on the diversity of the faecal microbiota and there was no statistically significant effect on CVD markers. A trend towards reduced oxidized LDL cholesterol following OEP ingestion was observed. At the genus level lactobacilli and Ruminococcus were reduced in OEP compared to CTRL biscuits. A trend towards increased bifidobacteria abundance was observed after OEP ingestion in 16S rRNA profiles, by fluorescent in situ hybridization and by qPCR. Targeted LC–MS revealed significant increases phenolic acid concentrations in 24-h urine following OEP ingestion and 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid, derivatives of hydroxytyrosol, were elevated in blood. A sex effect was apparent in urine small phenolic acid concentrations, and this sex effect was mirrored by statistically significant differences in relative abundances of faecal bacteria between men and women.ConclusionIngestion of OEP biscuits led to a significant increase in the metabolic output of the gut microbiota with an apparent sex effect possibly linked to differences in microbiota makeup. Increased levels of homovanillic acid and DOPAC, thought to be involved in reducing oxidative LDL cholesterol, were observed upon OEP ingestion. However, OEP did not induce statistically significant changes in either ox-LDL or urinary isoprostane in this study.

Highlights

  • Olives and olive oil are important and characteristic components of the Mediterranean diet, a dietary pattern shown to improve on both physical and mental quality of life, and reduce the risk of chronic diet-associated disease, especially cardiovascular disease (CVD) [1]

  • European Food Safety Authority (EFSA) considers that the claim that “consumption of olive oil polyphenols contributes to the protection of blood lipids from oxidative damage” reflects the scientific evidence, and that a dose of 5 mg of hydroxytyrosol and its derivatives in olive oil should be consumed daily for food products to bear the health claim

  • One recent study has shown that thyme phenolic compounds at different doses in olive oil can induce a small increase in bifidobacteria using the quantitative culture-independent method fluorescent in situ hybridization (FISH), with the suggestion that this change in microbiota could be related to improved LDL cholesterol oxidative status [21]

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Summary

Introduction

Olives and olive oil are important and characteristic components of the Mediterranean diet, a dietary pattern shown to improve on both physical and mental quality of life, and reduce the risk of chronic diet-associated disease, especially cardiovascular disease (CVD) [1]. Olive extracts have been found to induce acute reductions in arterial stiffness [11], which agrees with data suggesting that olive oil and olive extract significantly improve vascular function [12, 13] and blood pressure [14]. One recent study has shown that thyme phenolic compounds at different doses in olive oil can induce a small increase in bifidobacteria using the quantitative culture-independent method fluorescent in situ hybridization (FISH), with the suggestion that this change in microbiota could be related to improved LDL cholesterol oxidative status [21]. No studies have reported whether olives or olive pomace can impact on the relative abundances of the human gut microbiota, on the diversity of the gut microbiota and only a few studies have addressed the metabolic end products produced by combined host–microbiota cometabolism of olive polyphenols [20, 21]

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