Michelle C. McKinley

Dietary Intake of Fruits and Vegetables Improves Microvascular Function in Hypertensive Subjects in a Dose-Dependent Manner

Background— Observational evidence has consistently linked increased fruit and vegetable consumption with reduced cardiovascular morbidity; however, there is little direct trial evidence to support the concept that fruit and vegetable consumption improves vascular function. This study assessed the dose-dependent effects of a fruit and vegetable intervention on arterial health in subjects with hypertension. Methods and Results— After a 4-week run-in period during which fruit and vegetable intake was limited to 1 portion per day, participants were randomized to consume either 1, 3, or 6 portions daily for the next 8 weeks. Endothelium-dependent and -independent arterial vasodilator responses were assessed by venous occlusion plethysmography in the brachial circulation before and after intervention. Compliance was monitored with serial contemporaneous 4-day food records and by measuring concentrations of circulating dietary biomarkers. A total of 117 volunteers completed the 12-week study. Participants in the 1-, 3-, and 6-portions/d groups reported consuming on average 1.1, 3.2, and 5.6 portions of fruit and vegetables, respectively, and serum concentrations of lutein and &bgr;-cryptoxanthin increased across the groups in a dose-dependent manner. For each 1-portion increase in reported fruit and vegetable consumption, there was a 6.2% improvement in forearm blood flow responses to intra-arterial administration of the endothelium-dependent vasodilator acetylcholine (P=0.03). There was no association between increased fruit and vegetable consumption and vasodilator responses to sodium nitroprusside, an endothelium-independent vasodilator. Conclusions— The present study illustrates that among hypertensive volunteers, increased fruit and vegetable consumption produces significant improvements in an established marker of endothelial function and cardiovascular prognosis.

It's good to talk: children's views on food and nutrition

Objective:To gain an insight into childrens views about food and nutrition.Design:Data were collected in focus group discussions; two focus group sessions were undertaken with each school group.Setting:A total of 11 postprimary schools in Northern Ireland and England.Subjects:In all, 106 children aged 11–12-y-old (n=52 boys, n=54 girls).Results:Focus group transcripts were analysed using qualitative research methodology. Major barriers to healthy eating were taste, appearance of food, filling power, time/effort, cost, choice/availability, risk, rebellion, and body image/weight concerns. The main difference between sexes was in terms of motivating factors for eating well; girls tended to focus primarily on their appearance whereas boys appeared to be more influenced by sport. There was some mention of balance and variety within the focus group discussions, however, in practice, the children had a tendency to categorise foods as either ‘good’ or ‘bad’, ‘healthy’ or ‘unhealthy’.Conclusions:This study has revealed a number of barriers to, and motivations for, healthy eating, which should be taken into account when planning nutrition intervention strategies aimed at children moving into adolescence. While it may be possible to immediately attempt to address some of the barriers identified in this study, for example, in nutrition education initiatives, other barriers (such as the lack of available, attractive and affordable healthy foods in the school canteen) will prove more difficult to tackle without changes at the policy level. Overall, it appears that health promotion specialists have a major challenge ahead in order to encourage this age group to view healthy eating as an attractive and achievable behaviour.Sponsorship:Food Standards Agency, London, UK.

Low-fat versus low-carbohydrate weight reduction diets: effects on weight loss, insulin resistance, and cardiovascular risk: a randomized control trial.

OBJECTIVE Low-fat hypocaloric diets reduce insulin resistance and prevent type 2 diabetes in those at risk. Low-carbohydrate, high-fat diets are advocated as an alternative, but reciprocal increases in dietary fat may have detrimental effects on insulin resistance and offset the benefits of weight reduction. RESEARCH DESIGN AND METHODS We investigated a low-fat (20% fat, 60% carbohydrate) versus a low-carbohydrate (60% fat, 20% carbohydrate) weight reduction diet in 24 overweight/obese subjects ([mean ± SD] BMI 33.6 ± 3.7 kg/m2, aged 39 ± 10 years) in an 8-week randomized controlled trial. All food was weighed and distributed, and intake was calculated to produce a 500 kcal/day energy deficit. Insulin action was assessed by the euglycemic clamp and insulin secretion by meal tolerance test. Body composition, adipokine levels, and vascular compliance by pulse-wave analysis were also measured. RESULTS Significant weight loss occurred in both groups (P < 0.01), with no difference between groups (P = 0.40). Peripheral glucose uptake increased, but there was no difference between groups (P = 0.28), and suppression of endogenous glucose production was also similar between groups. Meal tolerance–related insulin secretion decreased with weight loss with no difference between groups (P = 0.71). The change in overall systemic arterial stiffness was, however, significantly different between diets (P = 0.04); this reflected a significant decrease in augmentation index following the low-fat diet, compared with a nonsignificant increase within the low-carbohydrate group. CONCLUSIONS This study demonstrates comparable effects on insulin resistance of low-fat and low-carbohydrate diets independent of macronutrient content. The difference in augmentation index may imply a negative effect of low-carbohydrate diets on vascular risk.

Sex hormone binding globulin and insulin resistance

Sex hormone binding globulin (SHBG) is a glycoprotein composed of two 373‐amino‐acid subunits. The SHBG gene and a promotor region have been identified. The SHBG receptor has yet to be cloned but is known to act through a G‐protein‐linked second‐messenger system following plasma membrane binding. The principal function of SHBG has traditionally been considered to be that of a transport protein for sex steroids, regulating circulating concentrations of free (unbound) hormones and their transport to target tissues. Recent research suggests that SHBG has functions in addition to the binding and transport of sex steroids. Observational studies have associated a low SHBG concentration with an increased incidence of type 2 diabetes mellitus (DM) independent of sex hormone levels in men and women. Genetic studies using Mendelian randomization analysis linking three single nucleotide polymorphisms of the SHBG gene to risk of developing type 2 DM suggest SHBG may have a role in the pathogenesis of type 2 DM. The correlation between SHBG and insulin resistance that is evident in a number of cross‐sectional studies is in keeping with the suggestion that the association between SHBG and incidence of type 2 DM is explained by insulin resistance. Several potential mechanisms may account for this association, including the identification of dietary factors that influence SHBG gene transcription. Further research to characterize the SHBG‐receptor and the SHBG second messenger system is required. An interventional study examining the effects on insulin resistance of altering SHBG concentrations may help in determining whether this association is causal.

Fruit and vegetable intake and risk of cardiovascular disease

A high intake of fruit and vegetables (FV) has been shown to be associated with reduced risk of a number of chronic diseases, including CVD. This review aims to provide an overview of the evidence that increased FV intake reduces risk of CVD, focusing on studies examining total FV intake. This evidence so far available is largely based on prospective cohort studies, with meta-analyses demonstrating an association between increased FV intake and reduced risk of both CHD and stroke. Controlled intervention trials examining either clinical or cardiovascular risk factor endpoints are scarce. However, such trials have shown that an increase in FV consumption can lower blood pressure and also improve microvascular function, both of which are commensurate with a reduced risk of CVD. The effects of increased FV consumption on plasma lipid levels, risk of diabetes and body weight have yet to be firmly established. In conclusion, evidence that FV consumption reduces the risk of CVD is so far largely confined to observational epidemiology, with further intervention studies required.

The relationship between breastfeeding and postpartum weight change—a systematic review and critical evaluation

Pregnancy and the postpartum period is a time of increased vulnerability for retention of excess body fat in women. Breastfeeding (BF) has been shown to have many health benefits for both mother and baby; however, its role in postpartum weight management is unclear. Our aim was to systematically review and critically appraise the literature published to date in relation to the impact of BF on postpartum weight change, weight retention and maternal body composition. Electronic literature searches were carried out using MEDLINE, EMBASE, PubMed, Web of Science, BIOSIS, CINAHL and British Nursing Index. The search covered publications up to 12 June 2012 and included observational studies (prospective and retrospective) carried out in BF mothers (either exclusively or as a subgroup), who were ⩽2 years postpartum and with a body mass index (BMI) >18.5 kg m–2, with an outcome measure of change in weight (including weight retention) and/or body composition. Thirty-seven prospective studies and eight retrospective studies were identified that met the selection criteria; studies were stratified according to study design and outcome measure. Overall, studies were heterogeneous, particularly in relation to sample size, measurement time points and in the classification of BF and postpartum weight change. The majority of studies reported little or no association between BF and weight change (n=27, 63%) or change in body composition (n=16, 89%), although this seemed to depend on the measurement time points and BF intensity. However, of the five studies that were considered to be of high methodological quality, four studies demonstrated a positive association between BF and weight change. This systematic review highlights the difficulties of examining the association between BF and weight management in observational research. Although the available evidence challenges the widely held belief that BF promotes weight loss, more robust studies are needed to reliably assess the impact of BF on postpartum weight management.

Biomarkers of Fruit and Vegetable Intake in Human Intervention Studies: A Systematic Review

Observational evidence consistently shows that consumption of a diet rich in fruit and vegetables may offer protection against diseases such as cardiovascular disease and cancer. Assessment of dietary intake is complex and prone to many sources of error. More objective biomarkers of fruit and vegetable intake are therefore of interest. The aim of this review is to examine the usefulness of the main biomarkers of fruit and vegetable intake to act as objective indicators of compliance in dietary intervention studies. A comprehensive search of the literature was conducted using six databases. Suitable papers were selected and relevant data extracted. The papers were categorized into 3 sub-groups: whole diet interventions; mixed fruit and vegetable interventions; and studies involving individual varieties of fruits or vegetables. Ninety-six studies were included in the review. Overall, the most commonly measured, and most consistently responsive, biomarkers were the carotenoids and vitamin C. Based on the results of this systematic review, it remains prudent to measure a panel of biomarkers in fruit and vegetable intervention studies. The only possible exception to this is “fruit only” intervention studies where assessment of vitamin C alone may suffice.

An evaluation of the sensitivity and specificity of energy expenditure measured by heart rate and the Goldberg cut-off for energy intake: basal metabolic rate for identifying mis-reporting of energy intake by adults and children: a retrospective analysis.

Objective: To identify adults and children as under- (UR), acceptable (AR), or over-reporters (OR) of energy intake (EI) using energy expenditure measured by doubly labelled water (DLW) (EEDLW), and to use this as a reference to determine the sensitivity and specificity of (i) EE measured by heart rate (EEHR), and (ii) the Goldberg cut-off technique for classifying subjects into the same categories.Design: Retrospective analysis of a dataset comprising concurrent measurements of EEDLW, EEHR, basal metabolic rate (BMR), and EI by weighed record (EIWR) on 14 adults and 36 children. EI by diet history (EIDH) was also measured in the children only. EIWR:EEDLW provided the reference definition of subjects as UR, AR or OR. Three strategies for classifying mis-reporters based on EEHR and Goldberg cut-offs were then explored. Sensitivity and specificity were calculated respectively as the proportion of UR and non-UR correctly identified.Results: Approximately 80% of all subjects were AR. For EIWR and EIDH respectively, the sensitivity of EEHR was 0.50 and 1.00, and specificity was 0.98 and 1.00. Although designating subjects as having low, medium or high activity levels (EEHR:BMRmeas) and calculating cut-offs based on appropriate WHO physical activity level PALs did not change sensitivity, specificity dropped to 0.98 (EIWR) and 0.97 (EIDH). Cut-offs based on a PAL of 1.55 reduced sensitivity to 0.33 (EIWR) and 0.00 (EIDH), but specificity remained unchanged. The sensitivity of all cut-offs based on physical activity level (PALs) for EIWR was 0.50 (adults) and 0.25 (children).Conclusions: If the precision of EEHR was improved, it may be useful for identifying mis-reporters of EI.

The Role of Micronutrients in Heart Failure

Heart failure is a common condition in the Western world, particularly among elderly persons and with an ever-aging population, the incidence is expected to increase. Diet in the setting of heart failure is important--patients with this condition are advised to consume a low-salt diet and monitor their weight closely. Nutritional status of patients with heart failure also is important--those with poor nutritional status tend to have a poor long-term prognosis. A growing body of evidence suggests an association between heart failure and micronutrient status. Reversible heart failure has been described as a consequence of severe thiamine and selenium deficiency. However, contemporary studies suggest that a more subtle relationship may exist between micronutrients and heart failure. This article reviews the existing literature linking heart failure and micronutrients, examining studies that investigated micronutrient intake, micronutrient status, and the effect of micronutrient supplementation in patients with heart failure, and focusing particularly on vitamin A, vitamin C, vitamin E, thiamine, other B vitamins, vitamin D, selenium, zinc, and copper.

Fruits and vegetables: measuring intake and encouraging increased consumption

A high intake of fruit and vegetables (FV) is associated with reduced risk of chronic disease, although the evidence base is mostly observational. Blood biomarkers offer an objective indicator of FV intake, potentially improving estimates of intakes based on traditional methods. A valid biomarker of overall FV intake would be able to confirm population intakes, more precisely evaluate the association between intakes and health outcomes and confirm compliance in FV interventions. Several substances have been proposed as biomarkers of FV intake: vitamin C, the carotenoids and polyphenols. Certain biomarkers are strong predictors of single FV; however, the proposed single biomarkers of FV consumption are only modestly predictive of overall FV consumption. This is likely to be due to the complexity of the FV food group. While accurately measuring FV intake is important in nutrition research, another critical question is: how best can an increase in FV intake be achieved? Increased FV intake has been achieved in efficacy studies using intensive dietary advice. Alternative, less intensive methods for encouraging FV consumption need to be developed and tested for population level intervention. Systematic reviews suggest peer support to be an effective strategy to promote dietary change. This review will describe the evidence for a link between increased FV intake and good health, outline possible novel biomarkers of FV consumption, present the most recently available data on population intake of FV and examine the usefulness of different approaches to encourage increased consumption of FV.