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Health Benefits of Dietary Whole Grains: An Umbrella Review of Meta-analyses
Abstract
Objective:
The purpose of this study is to review the effectiveness of the role of whole grain as a therapeutic agent in type 2 diabetes, cardiovascular disease, cancer, and obesity.
Methods:
An umbrella review of all published meta-analyses was performed. A PubMed search from January 1, 1980, to May 31, 2016, was conducted using the following search strategy: (whole grain OR whole grains) AND (meta-analysis OR systematic review). Only English language publications that provided quantitative statistical analysis on type 2 diabetes, cardiovascular disease, cancer, and weight loss were retrieved.
Results:
Twenty-one meta-analyses were retrieved for inclusion in this umbrella review, and all the meta-analyses reported statistically significant positive benefits for reducing the incidence of type 2 diabetes (relative risk [RR] = 0.68-0.80), cardiovascular disease (RR = 0.63-0.79), and colorectal, pancreatic, and gastric cancers (RR = 0.57-0.94) and a modest effect on body weight, waist circumference, and body fat mass. Significant reductions in cardiovascular and cancer mortality were also observed (RR = 0.82 and 0.89, respectively). Some problems of heterogeneity, publication bias, and quality assessment were found among the studies.
Conclusion:
This review suggests that there is some evidence for dietary whole grain intake to be beneficial in the prevention of type 2 diabetes, cardiovascular disease, and colorectal, pancreatic, and gastric cancers. The potential benefits of these findings suggest that the consumption of 2 to 3 servings per day (~45 g) of whole grains may be a justifiable public health goal.
... Regular consumption of whole grains has been associated with health benefits, such as the reduced risk of developing cardiovascular and other non-communicable diseases (McRae 2017). These health-promoting effects seem to be also correlated to their phytochemical composition (e.g.: PC, terpenes, alkylresorcinols) and the role of these molecules in the organism, and not only correlated to fibers and vitamins (McRae 2017;Shewry and Hey 2015). ...
... Regular consumption of whole grains has been associated with health benefits, such as the reduced risk of developing cardiovascular and other non-communicable diseases (McRae 2017). These health-promoting effects seem to be also correlated to their phytochemical composition (e.g.: PC, terpenes, alkylresorcinols) and the role of these molecules in the organism, and not only correlated to fibers and vitamins (McRae 2017;Shewry and Hey 2015). Although the mechanisms and the long-term effects are not yet fully understood, the consumption of PC in whole grains might provide effects even without being absorbed by the organism, such as in the carbohydrate metabolism pathway (e.g., reduction of the glycemic index and intestinal glucose absorption) and in the modulation of the intestinal microbiota (Giuberti et al. 2020). ...
Unlabelled:
Common wheat (Triticum aestivum) is one of the most consumed staple foods used for bakery products. Outer layers of grain present a great diversity of bioactive compounds, especially phenolic compounds (PC). Free and bound PC were extracted from eight genotypes of whole wheat flours (WWF) presenting different technological classifications. These extracts were comprehensively characterized through untargeted metabolomics applying ultra-high-performance liquid chromatography-mass spectrometry (UHPLC-MSE) and spectrophotometric analyses. Chemical composition and colorimetry were also determined by classical analyses. Thirty-eight PC were tentatively identified by UHPLC-MSE belonging to three classes (phenolic acids, flavonoids, and other polyphenols), some of them identified in all WWF samples. Bound hydroxycinnamic acids were the main PC found in WWF, especially the trans-ferulic acid and its isomer. No difference was found in starch and protein contents, whereas low-quality flours showed a higher ash content than the superior and medium-quality flours. Total phenolic content (TPC) ranged between 124.5 and 171.4 mg GAE/100 g WWF, which bound PC were responsible for 60% of TPC. Omics data and multivariate statistical analyses were successfully applied to discern the phenolic profile of WWF from different genotypes and technological qualities.
Supplementary information:
The online version contains supplementary material available at 10.1007/s13197-023-05665-8.
... Federal policy could encourage the service of low-impact lunches by increasing the requirements for whole grains. Whole grains are a nutritious, low-cost, diverse, and versatile food group that might offer solutions to the tradeoffs commonly confronted when proposing the consumption of sustainable diets 35,36 . We observed no difference in refined grain content of low and high-impact lunches; therefore, an increase in the whole grain requirement would not be associated with changes to refined grains. ...
... If limits on the servings of beef are put in place, grains, nuts and seeds, and seafood might be strong potential replacements given their nutritional composition and potential to provide Table 3 Use of proxies in linkages to FCID and percent contribution of proxies to total impacts, by food group. 35,41,42 . However, cost differentials might make this prohibitive in some circumstances, and new recipes incorporating these foods into entrées will be necessary. ...
Altering dietary patterns is essential to ameliorating the environmental impacts of the world food system. The U.S. National School Lunch Program shapes the consumption of America’s children and adolescents, providing a meaningful opportunity to reduce dietary environmental impacts. Here, we collate life cycle inventories relevant to the National School Lunch Program and assess the environmental impacts of a representative sample of lunches served in the U.S. during the 2014–2015 school year to inform school meal policy. The mean ± SE impact per lunch was 1.5 ± 0.03 kg CO2 eq. climate change, 1.8 ± 0.03 m²a crop eq. land use, 0.055 ± 0.00 m³ water consumption, and 0.24 ± 0.05 g phosphorus eq. freshwater and 3.1 ± 0.00 g nitrogen eq. marine eutrophication. Meat products contributed the most (28–67%) to total impacts for all impact categories. Lunches in the top quintile of impacts contributed an outsized proportion to total impacts (~40%) suggesting that policy changes related to these lunches should be prioritized. To reduce the environmental impacts of the National School Lunch Program, our results support increasing whole grain requirements and providing serving size or frequency limits for beef.
... Existe evidencia de las ventajas que proporciona su consumo por su elevado contenido de micronutrientes, fibra, germen y salvado (Barrett et al., 2019;Gain et al., 2012;Wu et al., 2020). Revisiones sistemáticas y meta-análisis vinculan el alto consumo de granos enteros con una menor incidencia y mortalidad por ECV (AlEssa et al., 2018;Aune et al., 2016;Reynolds et al., 2019;Slavin, 2008), por ejemplo, un consumo de granos enteros entre 210-225 g/día se ha asociado con una menor incidencia en enfermedad coronaria, accidente cerebrovascular, cáncer, muertes por todas las causas, enfermedad respiratoria, enfermedades infecciosas, DM2, enfermedades del sistema nervioso y muertes por todas las causas (Aune et al., 2016;Barrett et al., 2019;Gain et al., 2012;Mcrae, 2017;Tang et al., 2015). ...
... La relación positiva con la salud parece estar mediada por el contenido vitaminas, minerales y fitoquímicos que poseen propiedades anticancerígenas, principalmente contra el cáncer de tipo colorrectal (Aune & Chan, 2011;Mcrae, 2017). Los granos enteros, junto con las frutas y los vegetales son catalogados por la OMS como alimentos que deben incluirse como parte de una alimentación saludable que previene la aparición de las ECNT (Tang et al., 2015). ...
Introducción: En la población costarricense los carbohidratos son la principal fuente de
energía en la alimentación, y dado su conocido efecto en la salud resulta fundamental su estudio. Una estrategia para reducir las ECNT es brindar recomendaciones de macronutrientes, es por ello, que en este estudio se propuso una nueva metodología para evaluar los carbohidratos a partir de cuatro componentes: fibra dietética (g/d), radio granos enteros/granos totales, radio carbohidratos sólidos/sólidos+líquidos e índice glicémico. Este constituye el primer estudio del Índice de Calidad de los Carbohidratos en el país.
Objetivo: determinar la asociación entre el índice de calidad de los carbohidratos (ICC)
de la dieta y las características sociodemográficas, las medidas antropométricas y la actividad física en la población urbana costarricense entre los 15 y 65 años durante el 2014 y 2015.
Metodología: los datos provienen del Estudio Latinoamericano de Nutrición y Salud
(ELANS) del capítulo de Costa Rica. En una muestra de 798 personas según el sexo, grupo de edad (15-65 años), nivel económico y educativo, las variables antropométricas y el nivel de actividad física. El consumo de alimentos se obtuvo mediante la aplicación de dos recordatorios de 24 horas.
Resultados: el principal predictor de la calidad de los carbohidratos fue la fibra (=0.445),
seguido de los carbohidratos líquidos (=-0.426), los granos enteros (=0.374) y el índice
glicémico (=-0.357), (R2=0,721, p<0,001). El ICC fue significativamente mayor en los
hombres y en las personas de 20 a 65 años (p<0.001). Al ajustar por edad el ICC fue presentó una correlación débil para el índice de masa corporal (p<0.001) y las circunferencias de cadera (p=0,016) y cintura (p=0,022). No se encontraron diferencias significativas entre el ICC según el nivel de actividad física.
Conclusiones: en la población urbana costarricense un mayor ICC se relacionó con
mejores indicadores antropométricos, por lo que se deben establecer pautas dietéticas en función de carbohidratos con beneficios en la salud de las personas, y que se adapten a cultura alimentaria del país.
... The in vitro and animal studies provide some evidence that antioxidants are beneficial for health and, consequently, the increase in antioxidants content has been pursued particularly in cereals and Solanaceae, since they represent relevant dietary sources of nutrients in the human diet. A plethora of scientific evidence, summarized in Table 5, suggests that increased consumption of fruits, vegetables and cereals represents an easy and practical strategy to significantly reduce the incidence of chronic diseases, such as cancer, cardiovascular diseases, type-2 diabetes, obesity, and other aging-related pathologies [250][251][252][253][254][255][256][257][258][259][260]. A large population-based study (i.e., 24,325 men and women aged ≥35 years) has evidenced that a high polyphenol antioxidant content (PAC) score in the diet [261] is associated in both genders with low-grade inflammation, evaluated as C-Reactive Protein levels, white blood cells, platelet count, and granulocyte to lymphocyte ratio [262], with a reduced mortality risk, including cerebrovascular and cancer mortality [263], and with a decelerated biological aging [264]. ...
... Nevertheless, the potential impact of antioxidant-rich cultivars in comparison with conventional cultivars in the context of a generally healthy diet have been studied so far in very few clinical studies and deserves further investigation. Much evidence supports the potential beneficial properties of whole grain cereals, a result associated to their unique composition in vitamins and minerals, unsaturated fatty acids, tocotrienols, tocopherols, soluble and insoluble fiber, phytosterols, stanols, sphingolipids, phytates, lignans, and lipophilic and hydrophilic antioxidants, such as phenolic acids [46,259,[266][267][268]. The synergistic effect of these compounds, along with other nutrients, is responsible for health benefits associated to whole grain cereals [269]. ...
Given the general beneficial effects of antioxidants-rich foods on human health and disease prevention, there is a continuous interest in plant secondary metabolites conferring attractive colors to fruits and grains and responsible, together with others, for nutraceutical properties. Cereals and Solanaceae are important components of the human diet, thus, they are the main targets for functional food development by exploitation of genetic resources and metabolic engineering. In this review,
we focus on the impact of antioxidants-rich cereal and Solanaceae derived foods on human health by analyzing natural biodiversity and biotechnological strategies aiming at increasing the antioxidant level of grains and fruits, the impact of agronomic practices and food processing on antioxidant properties combined with a focus on the current state of pre-clinical and clinical studies. Despite the strong evidence in in vitro and animal studies supporting the beneficial effects of antioxidants-rich diets in preventing diseases, clinical studies are still not sufficient to prove the impact of antioxidant rich cereal and Solanaceae derived foods on human.
... Whole grains also contain a considerable amount of fibre, which partially explains our participants' low dietary fibre intake. These health advantages of whole grain warrant its preference over refined grain in a healthy diet (44,45) . In other FBDGs, a clear recommendation of whole grain intake was made that 90 g of whole grain products should be consumed daily and they should replace refined grain products (34) . ...
Poor dietary quality is a major contributor to malnutrition and disease burden in Vietnam, necessitating the development of a tool for improving dietary quality. Food-based dietary guidelines (FBDGs) have been proposed to do this by providing specific, culturally appropriate and actionable recommendations. We developed the Vietnamese Healthy Eating Index (VHEI) to assess the adherence to the 2016-2020 Vietnamese FBDGs and the dietary quality of the general Vietnamese population. This VHEI consists of eight component scores, 'grains', 'protein foods', 'vegetables', 'fruits', 'dairy', 'fats and oils', 'sugar and sweets' and 'salt and sauces', representing the recommendations in the FBDGs. Each component score ranges from 0 to 10, resulting in a total VHEI score between 0 (lowest adherence) and 80 (highest adherence). The VHEI was calculated using dietary intake data from the Vietnamese General Nutrition Survey 2009-2010 (n = 8225 households). Associations of the VHEI with socio-demographic characteristics, energy and nutrient intakes and food group consumptions were examined. The results showed that the mean and standard deviation score of the VHEI was 43⋅3 ± 8⋅1. The component 'sugar and sweets' scored the highest (9⋅8 ± 1⋅1), whereas the component 'dairy' scored the lowest (0⋅6 ± 1⋅6). The intake of micronutrients was positively associated with the total VHEI, both before and after adjustment for energy intake. In conclusion, the VHEI is a valuable measure of dietary quality for the Vietnamese population regarding their adherence to the FBDGs.
... It has been established that dietary food patterns play an important role in our health and wellbeing. Consumption of fruits, vegetables, whole grains and plant-based protein sources are proven to provide long-term health benefits [1][2][3][4]. Cereal grains and pulses are primary staple foods around the world, contributing to more than half of all calories and a significant portion of protein intake. A large body of evidence demonstrates that regular consumption of whole grains and pulses confers protective effects against various chronic diseases including obesity [5,6], type 2 diabetes (T2D) [7,8], cardiovascular disease (CVD) [9,10] and cancer [11,12]. ...
Pulses and whole grains are considered staple foods that provide a significant amount of calories, fibre and protein, making them key food sources in a nutritionally balanced diet. Additionally , pulses and whole grains contain many bioactive compounds such as dietary fibre, resistant starch, phenolic compounds and mono-and polyunsaturated fatty acids that are known to combat chronic disease. Notably, recent research has demonstrated that protein derived from pulse and whole grain sources contains bioactive peptides that also possess disease-fighting properties. Mechanisms of action include inhibition or alteration of enzyme activities, vasodilatation, modulation of lipid metabolism and gut microbiome and oxidative stress reduction. Consumer demand for plant-based proteins has skyrocketed primarily based on the perceived health benefits and lower carbon footprint of consuming foods from plant sources versus animal. Therefore, more research should be invested in discovering the health-promoting effects that pulse and whole grain proteins have to offer.
... Considering glycemic index, whole wheat bread is recommended over the white bread (Nirmala Prasadi and Joye 2020; Romão et al. 2021). It is assumed that the mechanism of action of wholegrains is associated with their dietary fibres promoting satiety and contributing into lipogenesis and fat storage (McRae 2017). Several studies reported contradictory results, where some findings sustained that no significant difference between refined white bread and whole wheat bread (Jenkins et al. 1988;Zafar et al. 2020), while other reported a lower glycemic index in wholegrain breads (Avber sek Lu znik et al. 2019). ...
Despite the importance of breads through the history, the wide range of options might lead to a choice dilemma from health-conscious consumers when purchasing bread. In this study, commercial white, wholegrain and multigrain regular breads, sold in Europe, were collected, and classified into gluten-free and gluten-containing categories. For gluten-free-breads, no significant differences were found in energy, saturated fatty acids, sugar, fibre and salt between white and wholegrain breads regardless of the mention "multigrain." For gluten-containing, carbohydrates and fibres differed between white and wholegrain breads, while when considering multigrain presence all the nutritional composition varied significantly. Nevertheless, the mentions whole-grain and multigrain on gluten-free and gluten-containing breads do not guarantee a better nutritional quality compared to white bread. Gluten-free breads showed increased fibre, and decreased carbohydrates, sugar and energy which are comparable to gluten-containing whole-grain breads. This underlines the improvement of gluten-free breads and suggests further investigations to increase protein content.
... Whole grains are a major supply of dietary fibre and are also enriched with vitamins, minerals and phyto-chemicals (McRae, 2017). Several studies have reported that elevated consumption of whole grains might bring about numerous health benefits to an individual (Kyro and Tjønneland, 2016;Seal et al., 2021). ...
Purpose
The paper aimed to explore the factors leading to lower rates of whole grain consumption amongst the Malaysian adult population according to the Reasoned Action Approach (RAA) model.
Design/methodology/approach
This paper employed a qualitative approach to explore the factors that influence whole grain consumption. Individual interviews were conducted online amongst Malaysian adults aged 18 years and above who purchase groceries and are responsible for food preparation at home. Interviews were transcribed verbatim and analysed thematically using the NVivo version 12 software.
Findings
A majority of the respondents ( N = 30; mean age = 39.2 years old) were females ( n = 19, 63.3%) and lived in urban areas ( n = 23, 76.7%). Even though over 86.7% of respondents ( n = 26) had consumed whole grain products, a majority of them had inadequate knowledge surrounding whole grains ( n = 25, 83.3%). Predominant barriers to whole grain consumption were perceived cost ( n = 30, 100%), dislikes towards the sensory aspects of whole grain foods ( n = 28, 93.3%), inadequate knowledge in identifying whole grains in foods ( n = 25, 83.3%), poor awareness ( n = 25, 83.3%), lack of knowledge in preparation of whole grain foods ( n = 25, 83.3%), a wide variety of other tasty cuisine alternatives in Malaysia ( n = 25, 83.3%), low availability and accessibility of whole grain products ( n = 18, 60%), cultural eating behaviours ( n = 17, 56.7%) and family influence ( n = 16, 53.3%). Besides that, having a longer preparation time, restrictive diets and social influences were minor barriers.
Research limitations/implications
This study addresses the barriers that should be highlighted in future health educational interventions, and presents a challenge to the food industry to develop whole grain foods which are easily accepted by consumers.
Originality/value
This is the first paper to outline the factors associated with poor consumption of whole grains amongst the Malaysian adult population.
Consumption of food in its natural form has an inverse relationship with cardiometabolic risk factors; however, the relationship between consumption of unprocessed or minimally processed foods and the presence of cardiovascular diseases (CVD) remains unclear in individuals receiving secondary care for CVD. Thus, we aimed to evaluate the association between the consumption of unprocessed or minimally processed foods and the presence of CVD and cardiometabolic risk factors in individuals with established CVD. Baseline data from 2357 participants in a Brazilian multicentre study showed that the consumption of unprocessed or minimally processed foods corresponded to most of the daily caloric intake (69.3%). Furthermore, regression analyses showed that higher consumption of unprocessed or minimally processed foods (>78.0% of caloric intake) was associated with a lower prevalence of elevated waist circumference (WC1; PR: 0.889; CI: 0.822-0.961; WC2; PR: 0.914; CI: 0.873-0.957) and overweight (PR: 0.930; CI: 0.870-0.994), but also was associated with simultaneous occurrence of coronary and peripheral artery disease and stroke (OR: 2.802; CI: 1.241-6.325) when compared with a lower intake (<62.8% of caloric intake). These findings reinforce the importance of nutritional guidance that considers the profile of the target population and the composition and quality of the meals consumed.
Evidence has suggested that nutrition is a preventive factor against cardiovascular disease (CVD) risk. Because of a sharp growth in published meta-analyses and pooled analyses in recent years, a reassessment of old evidence is needed. We aimed to determine the level of evidence for the association between the consumption of different food groups/items and dietary fiber and the incidence risk of CVDs, hypertension, and atrial fibrillation from meta-analyses and pooled analyses of observational studies. Databases Scopus, PubMed/Medline, and Web of Science were searched for related studies. Fifty-eight articles met the inclusion criteria for evidence grading. In summary, grading the level of evidence showed a suggestive inverse association between the higher consumption of fruits, whole grains, fish, legumes, nuts, and dietary fibers with the incidence risk of hypertension and different types of CVD. Also, there was a probable inverse association between the higher consumption of total and low-fat dairy products and the risk of hypertension. Higher red meat consumption had a probable association with the increased risk of ischemic stroke. Higher consumption of processed meat and poultry also had a suggestive direct association with the incidence risk of stroke and hypertension. We have tried to present a comprehensive and useful overview of the level of evidence based on the most updated findings. The summary of results in the current umbrella review can be a helpful tool for nutritionists, dietitians, and researchers to establish new studies and identify research gaps in related issues.
Mounting evidence from epidemiology studies suggests that whole grain intake may reduce pancreatic cancer risk, but convincing evidence is scarce. We conducted a meta-analysis to assess the association between whole grain intake and pancreatic cancer risk.
Relevant observational studies were identified by searching PubMed, Embase, Scopus, and Cochrane library databases for the period from January 1980 to July 2015, with no restrictions. We calculated the summary odds ratios (ORs) for pancreatic cancer using random-effects model meta-analysis. Between-study heterogeneity was analyzed using the I2 statistic.
A total of 8 studies regarding whole grain intake were included in the meta-analysis. The pooled OR of pancreatic cancer for those with high versus low whole grain intake was 0.76 (95% confidence interval [CI], 0.64–0.91; P = 0.002). There was no significant heterogeneity across these studies (I² = 11.7%; Pheterogeneity = 0.339). In the subgroup analysis by geographic area, the summary ORs of developing pancreatic cancer were 0.64 (95% CI, 0.53–0.79; P < 0.001; I2 = 0%; Pheterogeneity = 0.482) in the United States (n = 4) and 0.95 (95% CI, 0.63–1.43; P = 0.803; I2 = 45.6%; Pheterogeneity = 0.175) in Europe (n = 2). In the subgroup analysis by type of whole grain, the summary ORs were 0.72 (95% CI, 0.60–0.87; P = .001; I2 = 0; Pheterogeneity = 0.876) for grains (n = 4) and 0.74 (95% CI, 0.27–2.02; P = 0.554; I2 = 86.3%; Pheterogeneity = 0.007) for wheat (n = 2).
A high intake of whole grains was associated with a reduced risk of pancreatic cancer. Because of the absent of more cohort studies, further prospective studies need to be conducted to ensure conclusions that are more robust.
The potential associations between dietary consumption of nitrates, nitrites, and nitrosamines and gastric cancer risk have been investigated by several studies, but yielded inconclusive results. We conducted a meta-analysis to provide a quantitative assessment of their relationships. Relevant articles were identified by a systematic literature searching of PubMed and Embase databases prior to August 2015. Random-effects models were employed to pool the relative risks. A total of 22 articles consisting of 49 studies-19 studies for nitrates, 19 studies for nitrites, and 11 studies for N-nitrosodimethylamine (NDMA)-were included. The summary relative risk of stomach cancer for the highest categories, compared with the lowest, was 0.80 (95% confidence interval (CI), 0.69-0.93) for dietary nitrates intake, 1.31 (95% CI, 1.13-1.52) for nitrites, and 1.34 (95% CI, 1.02-1.76) for NDMA (p for heterogeneity was 0.015, 0.013 and <0.001, respectively). The study type was found as the main source of heterogeneity for nitrates and nitrites. The heterogeneity for NDMA could not be eliminated completely through stratified analysis. Although significant associations were all observed in case-control studies, the cohort studies still showed a slight trend. The dose-response analysis indicated similar results as well. High nitrates intake was associated with a weak but statistically significant reduced risk of gastric cancer. Whereas increased consumption of nitrites and NDMA seemed to be risk factors for cancer. Due to the lack of uniformity for exposure assessment across studies, further prospective researches are warranted to verify these findings.
Background:
The relationships between dietary fiber, whole grains, carbohydrate, glycemic index (GI), glycemic load (GL), and prostate cancer risk are unclear. We conducted a systematic review and meta-analysis to investigate these associations.
Methods:
Relevant studies were identified by a search of PubMed database and EMBASE database up to April 2015. A random effects model was used to calculate the summary relative risks (RRs) and their corresponding 95% confidence intervals (CIs).
Results:
Twenty-seven epidemiological studies (18 case-control studies and nine cohort studies) were included in the final analysis. The pooled RRs of prostate cancer were 0.94 (95% CI 0.85-1.05, P=0.285), 1.13 (95% CI 0.98-1.30, P=0.095), 0.96 (95% CI 0.81-1.14, P=0.672), 1.06 (95% CI 0.96-1.18, P=0.254), and 1.04 (95% CI 0.91-1.18, P=0.590) for dietary fiber, whole grains, carbohydrate, GI, and GL, respectively. There was no evidence of significant publication bias based on the Begg's test and Egger's test.
Conclusion:
The findings of this meta-analysis indicate that, based on available information, dietary fiber, whole grains, carbohydrate, GI, and GL are not associated with the risk of prostate cancer.
Aims:
With the increase in the number of systematic reviews available, a logical next step to provide decision makers in healthcare with the evidence they require has been the conduct of reviews of existing systematic reviews. Syntheses of existing systematic reviews are referred to by many different names, one of which is an umbrella review. An umbrella review allows the findings of reviews relevant to a review question to be compared and contrasted. An umbrella review's most characteristic feature is that this type of evidence synthesis only considers for inclusion the highest level of evidence, namely other systematic reviews and meta-analyses. A methodology working group was formed by the Joanna Briggs Institute to develop methodological guidance for the conduct of an umbrella review, including diverse types of evidence, both quantitative and qualitative. The aim of this study is to describe the development and guidance for the conduct of an umbrella review.
Methods:
Discussion and testing of the elements of methods for the conduct of an umbrella review were held over a 6-month period by members of a methodology working group. The working group comprised six participants who corresponded via teleconference, e-mail and face-to-face meeting during this development period. In October 2013, the methodology was presented in a workshop at the Joanna Briggs Institute Convention. Workshop participants, review authors and methodologists provided further testing, critique and feedback on the proposed methodology.
Results:
This study describes the methodology and methods developed for the conduct of an umbrella review that includes published systematic reviews and meta-analyses as the analytical unit of the review. Details are provided regarding the essential elements of an umbrella review, including presentation of the review question in a Population, Intervention, Comparator, Outcome format, nuances of the inclusion criteria and search strategy. A critical appraisal tool with 10 questions to help assess risk of bias in systematic reviews and meta-analyses was also developed and tested. Relevant details to extract from included reviews and how to best present the findings of both quantitative and qualitative systematic reviews in a reader friendly format are provided.
Conclusions:
Umbrella reviews provide a ready means for decision makers in healthcare to gain a clear understanding of a broad topic area. The umbrella review methodology described here is the first to consider reviews that report other than quantitative evidence derived from randomized controlled trials. The methodology includes an easy to use and informative summary of evidence table to readily provide decision makers with the available, highest level of evidence relevant to the question posed.
Whole grains are recognized for their potential role in preventing cardiovascular diseases; however, results from randomized controlled studies on blood lipids are inconsistent, potentially because of compositional differences between individual grain types for some nutrients, including dietary fiber.
Using a meta-analytic approach, we assessed the effect of whole-grain compared with non-whole-grain foods on changes in total cholesterol (TC), LDL cholesterol, HDL cholesterol, and triglycerides.
We conducted a systematic literature search in selected databases. Studies were included if they were randomized controlled comparisons between whole-grain foods and a non-whole-grain control in adults. A total of 6069 articles were screened for eligibility, and data were extracted from 24 studies. Weighted mean differences were calculated, and meta-regression analyses were performed for whole-grain dose, study duration, and baseline TC concentration.
Overall, whole-grain intake lowered LDL cholesterol (weighted difference: -0.09 mmol/L; 95% CI: -0.15, -0.03 mmol/L; P < 0.01) and TC (weighted difference: -0.12 mmol/L; 95% CI: -0.19, -0.05 mmol/L; P < 0.001) compared with the control. Whole-grain oat had the greatest effect on TC (weighted difference: -0.17 mmol/L; 95% CI: -0.10, -0.25 mmol/L; P < 0.001). No effect of whole-grain foods on HDL cholesterol was seen, whereas whole-grain foods tended to lower triglycerides compared with the control (weighted difference: -0.04 mmol/L; 95% CI: -0.08, 0.01; P = 0.10). No association was found between whole-grain dose or baseline TC concentration and any of the outcomes, whereas study duration was positively associated with changes in TC and LDL cholesterol.
Consumption of whole-grain diets lowers LDL cholesterol and TC, but not HDL cholesterol or triglycerides, compared with consumption of non-whole-grain control diets. Whole-grain oat appears to be the most effective whole grain for lowering cholesterol.
© 2015 American Society for Nutrition.
Background:
The potential role of whole grain in preventing various mortality outcomes has been inconsistently reported in a wealth of prospective observational studies.
Objective:
We evaluated the relations between whole-grain intake and risks of dying from any cause, cardiovascular disease (CVD), and cancer through a meta-analytic approach.
Design:
Relevant studies were identified by searching PubMed and EMBASE databases and bibliographies of retrieved full publications. Summary RRs with 95% CIs were calculated with a random-effects model.
Results:
Thirteen studies on total mortality (104,061 deaths), 12 on CVD mortality (26,352 deaths), and 8 on cancer mortality (34,797 deaths) were included. Three studies reported whole-grain intake, and the remaining studies reported whole-grain product intake. In the dose-response analysis in which the intake of whole-grain products was converted to the amount of whole grain, the summary RRs for an increment in whole-grain intake of 50 g/d were 0.78 (95% CI: 0.67, 0.91) for total mortality, 0.70 (95% CI: 0.61, 0.79) for CVD mortality, and 0.82 (95% CI: 0.69, 0.96) for cancer mortality. A similar reduction was observed for the mortality from ischemic heart disease (RR: 0.68; 95% CI: 0.55, 0.84) but not from stroke (RR: 0.93; 95% CI: 0.54, 1.62). There was evidence of nonlinear associations of whole-grain intake with total (P-nonlinearity < 0.001) and CVD mortality (P-nonlinearity <0.001), but not with cancer mortality (P-nonlinearity = 0.12), with the curves for the associations appearing slightly steeper at lower ranges (<35 g/d) of the intake than at higher ranges.
Conclusions:
Our findings suggest significant inverse relationships between whole-grain intake and mortality due to any cause, CVD, or cancer. The findings support the recommendation of increasing whole-grain intake to improve public health.
Results of the relationships between dietary whole-grain consumption and the risk of all-cause, CVD and cancer-specific mortality are mixed. We summarised the evidence based on a meta-analysis of prospective cohort studies. Pertinent studies were identified by searching articles in the MEDLINE and EMBASE databases up to 20 January 2016 and by reviewing the reference lists of the retrieved articles. Random-effects models were used to calculate summary relative risks (SRR) and 95 % CI. In all, eleven prospective studies (ten publications) were included in the meta-analysis. There were a total of 816 599 subjects and 89 251 cases of all-cause mortality. On the basis of the highest
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the lowest categories of intake, whole grains may be associated with a lower risk of mortality from all causes (SRR 0·87; 95 % CI 0·84, 0·90), CVD (SRR 0·81; 95 % CI 0·75, 0·89) and all cancers (SRR 0·89; 95 % CI 0·82, 0·96). For each 3 servings/d increase in whole-grain intake, there was a 19 % reduction in the risk of all-cause mortality (SRR 0·81; 95 % CI 0·76, 0·85), a 26 % reduction in CVD mortality (SRR 0·74; 95 % CI 0·66, 0·83) and a 9 % reduction in cancer mortality (SRR 0·91; 95 % CI 0·84, 0·98). The current meta-analysis provides some evidence that high intake of whole grains was inversely associated with the risk of all-cause, CVD and cancer-specific mortality. Further well-designed studies, including clinical trials and in different populations, are required to confirm our findings.
The association between whole and refined grain consumption and stroke risk remains unclear. A search using MEDLINE and EMBASE databases was performed through February 29, 2016. Seven prospective studies with a total of 446 451 subjects and 5892 stroke events were included. The summary relative risk (SRR) of stroke for the high versus low consumption was 0.95 (95% confidence interval [CI] = 0.83-1.14) for total grains, 0.92 (95% CI = 0.72-1.17) for whole grains, and 0.99 (95% CI = 0.84-1.16) for refined grains. Diets rich in whole grains were inversely associated with ischemic stroke risk (SRR = 0.75, 95% CI = 0.60-0.95). Our meta-analysis revealed that whole and refined grain consumption is not associated with total stroke risk; however, whole grain consumption is associated with reduced ischemic stroke risk.
Background:
Researches of the relationships between dietary whole grains intake and risk of stroke have produced inconsistent results. We therefore conducted a meta-analysis to summarize the evidence from observed studies regarding the association between whole grain intake and stroke risk.
Methods:
Pertinent studies were identified by searching Web of Knowledge and PubMed up to May 2015. Random-effect model was used to combine the relative risk (RR) with the corresponding 95% confidence intervals (CI). Publication bias was estimated using Egger's regression asymmetry test.
Results:
Six prospective studies involving 1635 stroke cases and 247487 participants were included in this meta-analysis. Pooled results suggested that highest category of whole grain intake versus lowest category was significantly associated with reduced the risk of stroke [summary RR = 0.86, 95% CI = 0.73-0.99, I2 = 0.0%]. Inverse associations were also found in the America population [summary RR = 0.81, 95% CI = 0.67-0.98, I(2) = 0.0%] and subgroup analysis of females [summary RR = 0.78, 95% CI = 0.63-0.97, I(2) = 0.0%]. No publication bias was found.
Conclusion:
Our analysis indicated that higher whole grain intake has a protective effect on stroke.