Julie A. Lovegrove

Fruit polyphenols and CVD risk: a review of human intervention studies

Epidemiological evidence suggests that polyphenols may, in part, explain the cardioprotective properties of fruits. This review aims to summarise the evidence for the effects of fruit polyphenols on four risk factors of CVD: platelet function, blood pressure, vascular function and blood lipids. This review includes human dietary intervention studies investigating fruits and their polyphenols. There was some evidence to suggest that fruits containing relatively high concentrations of flavonols, anthocyanins and procyanindins, such as pomegranate, purple grapes and berries, were effective at reducing CVD risk factors, particularly with respect to anti-hypertensive effects, inhibition of platelet aggregation and increasing endothelial-dependent vasodilation than other fruits investigated. Flavanone-rich fruits, such as oranges and grapefruits, were reported to have hypocholesterolaemic effects, with little impact on other risk factors being examined. However, the evidence was limited, inconsistent and often inconclusive. This is in part due to the heterogeneity in the design of studies, the lack of controls, the relatively short intervention periods and low power in several studies. Details of the polyphenol content of the fruits investigated were also omitted in some studies, negating comparison of data. It is recommended that large, well-powered, long-term human dietary intervention studies investigating a wider range of fruits are required to confirm these observations. Investigations into the potential synergistic effects of polyphenols on a combination of CVD risk markers, dose-response relationships and standardisation in methodology would facilitate the comparison of studies and also provide valuable information on the types of fruits which could confer protection against CVD.

Effects of dietary fat modification on insulin sensitivity and on other risk factors of the metabolic syndrome--LIPGENE: a European randomized dietary intervention study.

Background:Excessive energy intake and obesity lead to the metabolic syndrome (MetS). Dietary saturated fatty acids (SFAs) may be particularly detrimental on insulin sensitivity (SI) and on other components of the MetS.Objective:This study determined the relative efficacy of reducing dietary SFA, by isoenergetic alteration of the quality and quantity of dietary fat, on risk factors associated with MetS.Design:A free-living, single-blinded dietary intervention study.Subjects and Methods:MetS subjects (n=417) from eight European countries completed the randomized dietary intervention study with four isoenergetic diets distinct in fat quantity and quality: high-SFA; high-monounsaturated fatty acids and two low-fat, high-complex carbohydrate (LFHCC) diets, supplemented with long chain n-3 polyunsaturated fatty acids (LC n-3 PUFAs) (1.2 g per day) or placebo for 12 weeks. SI estimated from an intravenous glucose tolerance test (IVGTT) was the primary outcome measure. Lipid and inflammatory markers associated with MetS were also determined.Results:In weight-stable subjects, reducing dietary SFA intake had no effect on SI, total and low-density lipoprotein cholesterol concentration, inflammation or blood pressure in the entire cohort. The LFHCC n-3 PUFA diet reduced plasma triacylglycerol (TAG) and non-esterified fatty acid concentrations (P<0.01), particularly in men.Conclusion:There was no effect of reducing SFA on SI in weight-stable obese MetS subjects. LC n-3 PUFA supplementation, in association with a low-fat diet, improved TAG-related MetS risk profiles.

Effect of changing the amount and type of fat and carbohydrate on insulin sensitivity and cardiovascular risk: the RISCK (Reading, Imperial, Surrey, Cambridge, and Kings) trial

BACKGROUND Insulin sensitivity (Si) is improved by weight loss and exercise, but the effects of the replacement of saturated fatty acids (SFAs) with monounsaturated fatty acids (MUFAs) or carbohydrates of high glycemic index (HGI) or low glycemic index (LGI) are uncertain. OBJECTIVE We conducted a dietary intervention trial to study these effects in participants at risk of developing metabolic syndrome. DESIGN We conducted a 5-center, parallel design, randomized controlled trial [RISCK (Reading, Imperial, Surrey, Cambridge, and Kings)]. The primary and secondary outcomes were changes in Si (measured by using an intravenous glucose tolerance test) and cardiovascular risk factors. Measurements were made after 4 wk of a high-SFA and HGI (HS/HGI) diet and after a 24-wk intervention with HS/HGI (reference), high-MUFA and HGI (HM/HGI), HM and LGI (HM/LGI), low-fat and HGI (LF/HGI), and LF and LGI (LF/LGI) diets. RESULTS We analyzed data for 548 of 720 participants who were randomly assigned to treatment. The median Si was 2.7 × 10(-4) mL · μU(-1) · min(-1) (interquartile range: 2.0, 4.2 × 10(-4) mL · μU(-1) · min(-1)), and unadjusted mean percentage changes (95% CIs) after 24 wk treatment (P = 0.13) were as follows: for the HS/HGI group, -4% (-12.7%, 5.3%); for the HM/HGI group, 2.1% (-5.8%, 10.7%); for the HM/LGI group, -3.5% (-10.6%, 4.3%); for the LF/HGI group, -8.6% (-15.4%, -1.1%); and for the LF/LGI group, 9.9% (2.4%, 18.0%). Total cholesterol (TC), LDL cholesterol, and apolipoprotein B concentrations decreased with SFA reduction. Decreases in TC and LDL-cholesterol concentrations were greater with LGI. Fat reduction lowered HDL cholesterol and apolipoprotein A1 and B concentrations. CONCLUSIONS This study did not support the hypothesis that isoenergetic replacement of SFAs with MUFAs or carbohydrates has a favorable effect on Si. Lowering GI enhanced reductions in TC and LDL-cholesterol concentrations in subjects, with tentative evidence of improvements in Si in the LF-treatment group. This trial was registered at clinicaltrials.gov as ISRCTN29111298.

Ingestion of quercetin inhibits platelet aggregation and essential components of the collagen-stimulated platelet activation pathway in humans

Summary.  Background: Quercetin, a flavonoid present in the human diet, which is found in high levels in onions, apples, tea and wine, has been shown previously to inhibit platelet aggregation and signaling in vitro. Consequently, it has been proposed that quercetin may contribute to the protective effects against cardiovascular disease of a diet rich in fruit and vegetables. Objectives: A pilot human dietary intervention study was designed to investigate the relationship between the ingestion of dietary quercetin and platelet function. Methods: Human subjects ingested either 150 mg or 300 mg quercetin‐4′‐O‐β‐D‐glucoside supplement to determine the systemic availability of quercetin. Platelets were isolated from subjects to analyse collagen‐stimulated cell signaling and aggregation. Results: Plasma quercetin concentrations peaked at 4.66 µm (± 0.77) and 9.72 µm (± 1.38) 30 min after ingestion of 150‐mg and 300‐mg doses of quercetin‐4′‐O‐β‐D‐glucoside, respectively, demonstrating that quercetin was bioavailable, with plasma concentrations attained in the range known to affect platelet function in vitro. Platelet aggregation was inhibited 30 and 120 min after ingestion of both doses of quercetin‐4′‐O‐β‐D‐glucoside. Correspondingly, collagen‐stimulated tyrosine phosphorylation of total platelet proteins was inhibited. This was accompanied by reduced tyrosine phosphorylation of the tyrosine kinase Syk and phospholipase Cγ2, components of the platelet glycoprotein VI collagen receptor signaling pathway. Conclusions: This study provides new evidence of the relatively high systemic availability of quercetin in the form of quercetin‐4′‐O‐β‐D‐glucoside by supplementation, and implicates quercetin as a dietary inhibitor of platelet cell signaling and thrombus formation.

The type and quantity of dietary fat and carbohydrate alter faecal microbiome and short-chain fatty acid excretion in a metabolic syndrome ‘at-risk’ population

INTRODUCTION AND OBJECTIVES:An obese-type human microbiota with an increased Firmicutes:Bacteroidetes ratio has been described that may link the gut microbiome with obesity and metabolic syndrome (MetS) development. Dietary fat and carbohydrate are modifiable risk factors that may impact on MetS by altering the human microbiome composition. We determined the effect of the amount and type of dietary fat and carbohydrate on faecal bacteria and short chain fatty acid (SCFA) concentrations in people ‘at risk’ of MetS.DESIGN:A total of 88 subjects at increased MetS risk were fed a high saturated fat diet (HS) for 4 weeks (baseline), then randomised onto one of the five experimental diets for 24 weeks: HS; high monounsaturated fat (MUFA)/high glycemic index (GI) (HM/HGI); high MUFA/low GI (HM/LGI); high carbohydrate (CHO)/high GI (HC/HGI); and high CHO/low GI (HC/LGI). Dietary intakes, MetS biomarkers, faecal bacteriology and SCFA concentrations were monitored.RESULTS:High MUFA diets did not affect individual bacterial population numbers but reduced total bacteria and plasma total and LDL-cholesterol. The low fat, HC diets increased faecal Bifidobacterium (P=0.005, for HC/HGI; P=0.052, for HC/LGI) and reduced fasting glucose and cholesterol compared to baseline. HC/HGI also increased faecal Bacteroides (P=0.038), whereas HC/LGI and HS increased Faecalibacterium prausnitzii (P=0.022 for HC/HGI and P=0.018, for HS). Importantly, changes in faecal Bacteroides numbers correlated inversely with body weight (r=−0.64). A total bacteria reduction was observed for high fat diets HM/HGI and HM/LGI (P=0.023 and P=0.005, respectively) and HS increased faecal SCFA concentrations (P<0.01).CONCLUSION:This study provides new evidence from a large-scale dietary intervention study that HC diets, irrespective of GI, can modulate human faecal saccharolytic bacteria, including bacteroides and bifidobacteria. Conversely, high fat diets reduced bacterial numbers, and in the HS diet, increased excretion of SCFA, which may suggest a compensatory mechanism to eliminate excess dietary energy.

Quercetin inhibits collagen-stimulated platelet activation through inhibition of multiple components of the glycoprotein VI signaling pathway

Summary.  Background: The regulation of platelet function by pharmacological agents that modulate platelet signaling has proven a successful approach to the prevention of thrombosis. A variety of molecules present in the diet have been shown to inhibit platelet activation, including the antioxidant quercetin. Objectives: In this report we investigate the molecular mechanisms through which quercetin inhibits collagen‐stimulated platelet aggregation. Methods: The effect of quercetin on platelet aggregation, intracellular calcium release, whole cell tyrosine phosphorylation and intracellular signaling events including tyrosine phosphorylation and kinase activity of proteins involved in the collagen‐stimulated glycoprotein (GP) signaling pathway were investigated. Results: We report that quercetin inhibits collagen‐stimulated whole cell protein tyrosine phosphorylation and intracellular mobilization of calcium, in a concentration‐dependent manner. Quercetin was also found to inhibit various events in signaling generated by the collagen receptor GPVI. This includes collagen‐stimulated tyrosine phosphorylation of the Fc receptor γ‐chain, Syk, LAT and phospholipase Cγ2. Inhibition of phosphorylation of the Fc receptor γ‐chain suggests that quercetin inhibits early signaling events following stimulation of platelets with collagen. The activity of the kinases that phosphorylate the Fc receptor γ‐chain, Fyn and Lyn, as well as the tyrosine kinase Syk and phosphoinositide 3‐kinase was also inhibited by quercetin in a concentration‐dependent manner, both in whole cells and in isolation. Conclusions: The present results provide a molecular basis for the inhibition by quercetin of collagen‐stimulated platelet activation, through inhibition of multiple components of the GPVI signaling pathway, and may begin to explain the proposed health benefits of high quercetin intake.

Use of manufactured foods enriched with fish oils as a means of increasing long-chain n −3 polyunsaturated fatty acid intake

The objectives of the present study were to determine the feasibility of using manufactured foods, enriched with eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) as a means of increasing the intake of these n-3 polyunsaturated fatty acids (PUFA), and to determine the effect of the consumption of these foods on postprandial lipaemia and other metabolic responses to a high-fat mixed test meal. Nine healthy, normotriacylglycerolaemic, free-living male volunteers (aged 35-60 years) completed the randomized, controlled, single-blind, crossover study. The study consisted of two periods (each of 22 d) of dietary intervention, separated by a 5-month washout period. During these two periods the subjects were provided with the manufactured foods enriched with EPA and DHA (n-3 enriched) or identical but unenriched foods (control). A mixed test meal containing 82 g fat was given to the fasted subjects on day 22 of each dietary intervention period. Two fasting, and thereafter hourly, blood samples were collected from the subjects for an 8 h period postprandially. Plasma triacylglycerol, total and HDL-cholesterol, non-esterified fatty acids (NEFA), glucose and immunoreactive insulin levels, post-heparin lipoprotein lipase (EC 3.1.1.34) activity and the plasma free fatty acid and phospholipid fatty acid compositions were measured. A mean daily intake of 1.4 g EPA+DHA (0.9 g EPA, 0.5 g DHA) was ingested during the n-3-enriched dietary period, which was significantly higher than the intake during the habitual and control periods (P < 0.001) assessed by a 3 d weighed food intake. A significantly higher level of EPA+DHA enrichment of the plasma fatty acids and phospholipids (P < 0.001) after the n-3-enriched compared with the control intervention periods was also found. The energy intake on both of the dietary intervention periods was found to be significantly higher than on the habitual diet (P < 0.001), with an increase in body weight of the subjects, which reached significance during the n-3 PUFA-enriched dietary intervention period (P < 0.04). The palatability of the enriched foods was not significantly different from that of the control foods. Significantly higher fasting plasma HDL-cholesterol and glucose concentrations were found after the n-3 PUFA-enriched compared with the control intervention period (P < 0.02 and P < 0.05 respectively). No significant differences were found for the postprandial lipid and hormone measurements, except for significantly lower levels of NEFA at 60 min after the n-3-enriched intervention period (P < 0.04). Enriched manufactured foods were a feasible vehicle for increasing n-3 PUFA intake. However the nature of the foods provided as the n-3 vehicle may have contributed to the increased body weight and higher energy intakes which were adverse consequences of the intervention. These factors, together with the short duration of the study may have been responsible for the failure to observe significant plasma triacylglycerol reductions in response to daily intakes of 1.4 g EPA+DHA.

UK Food Standards Agency Workshop Report: the effects of the dietary n-6:n-3 fatty acid ratio on cardiovascular health.

This report summarises a workshop convened by the UK Food Standards Agency (FSA) on 11 September 2006 to review the results of three FSA-funded studies and other recent research on effects of the dietary n-6:n-3 fatty acid ratio on cardiovascular health. The objective of this workshop was to reach a clear conclusion on whether or not it was worth funding any further research in this area. On the basis of this review of the experimental evidence and on theoretical grounds, it was concluded that the n-6:n-3 fatty acid ratio is not a useful concept and that it distracts attention away from increasing absolute intakes of long-chain n-3 fatty acids which have been shown to have beneficial effects on cardiovascular health. Other markers of fatty acid intake, that more closely relate to physiological function, may be more useful.

Flavonoid-rich fruit and vegetables improve microvascular reactivity and inflammatory status in men at risk of cardiovascular disease—FLAVURS: a randomized controlled trial

BACKGROUND Observed associations between increased fruit and vegetable (F&V) consumption, particularly those F&Vs that are rich in flavonoids, and vascular health improvements require confirmation in adequately powered randomized controlled trials. OBJECTIVE This study was designed to measure the dose-response relation between high-flavonoid (HF), low-flavonoid (LF), and habitual F&V intakes and vascular function and other cardiovascular disease (CVD) risk indicators. DESIGN A single-blind, dose-dependent, parallel randomized controlled dietary intervention study was conducted. Male and female low-F&V consumers who had a ≥ 1.5-fold increased risk of CVD (n = 174) were randomly assigned to receive an HF F&V, an LF F&V, or a habitual diet, with HF and LF F&V amounts sequentially increasing by 2, 4, and 6 (+2, +4, and +6) portions/d every 6 wk over habitual intakes. Microvascular reactivity (laser Doppler imaging with iontophoresis), arterial stiffness [pulse wave velocity, pulse wave analysis (PWA)], 24-h ambulatory blood pressure, and biomarkers of nitric oxide (NO), vascular function, and inflammation were determined at baseline and at 6, 12, and 18 wk. RESULTS In men, the HF F&V diet increased endothelium-dependent microvascular reactivity (P = 0.017) with +2 portions/d (at 6 wk) and reduced C-reactive protein (P = 0.001), E-selectin (P = 0.0005), and vascular cell adhesion molecule (P = 0.0468) with +4 portions/d (at 12 wk). HF F&Vs increased plasma NO (P = 0.0243) with +4 portions/d (at 12 wk) in the group as a whole. An increase in F&Vs, regardless of flavonoid content in the groups as a whole, mitigated increases in vascular stiffness measured by PWA (P = 0.0065) and reductions in NO (P = 0.0299) in the control group. CONCLUSION These data support recommendations to increase F&V intake to ≥ 6 portions daily, with additional benefit from F&Vs that are rich in flavonoids, particularly in men with an increased risk of CVD.

Blood pressure-lowering effects of beetroot juice and novel beetroot- enriched bread products in normotensive male subjects

A number of vegetables have a high nitrate content which after ingestion can be reduced to nitrite by oral bacteria, and further to vasoprotective NO endogenously. In the present study, two separate randomly controlled, single-blind, cross-over, postprandial studies were performed in normotensive volunteers. Ambulatory blood pressure (BP) was measured over a 24 h period following consumption of either four doses of beetroot juice (BJ), 0, 100, 250 and 500 g (n 18), or three bread products, control bread (0 g beetroot), red beetroot- and white beetroot-enriched breads (n 14). Total urinary nitrate/nitrite (NO(x)) was measured at baseline, and at 2, 4 and 24 h post-ingestion. BJ consumption significantly, and in a near dose-dependent manner, lowered systolic BP (SBP, P < 0·01) and diastolic BP (DBP, P < 0·001) over a period of 24 h, compared with water control. Furthermore, bread products enriched with 100 g red or white beetroot lowered SBP and DBP over a period of 24 h (red beetroot-enriched bread, P <0·05), with no statistical differences between the varieties. Total urinary NO(x) significantly increased following the consumption of 100 g (P < 0·01), 250 g (P <0·001) and 500 g BJ (P <0·001) and after red beetroot-enriched bread ingestion (P <0·05), but did not reach significance for white beetroot-enriched bread compared with the no-beetroot condition. These studies demonstrated significant hypotensive effects of a low dose (100 g) of beetroot which was unaffected by processing or the presence of betacyanins. These data strengthen the evidence for cardioprotective BP-lowering effects of dietary nitrate-rich vegetables.