Diet as one aspect of lifestyle is thought to be one of the modifiable risk factors for the development of type 2 diabetes mellitus (T2DM). Information is needed as to which components of the diet could be protective for this disease.
To asses the effects of whole-grain foods for the prevention of T2DM.
We searched CENTRAL, MEDLINE, EMBASE, CINAHL and AMED.
We selected cohort studies with a minimum duration of five years that assessed the association between intake of whole-grain foods or cereal fibre and incidence of T2DM. Randomised controlled trials lasting at least six weeks were selected that assessed the effect of a diet rich in whole-grain foods compared to a diet rich in refined grain foods on T2DM and its major risk factors.
Two authors independently selected the studies, assessed study quality and extracted data. Data of studies were not pooled because of methodological diversity.
One randomised controlled trial and eleven prospective cohort studies were identified. The randomised controlled trial, which was of low methodological quality, reported the change in insulin sensitivity in 12 obese hyperinsulinemic participants after six-week long interventions. Intake of whole grain foods resulted in a slight improvement of insulin sensitivity and no adverse effects. Patient satisfaction, health related quality of life, total mortality and morbidity was not reported. Four of the eleven cohort studies measured cereal fibre intake, three studies whole grain intake and two studies both. Two studies measured the change in whole grain food intake and one of them also change in cereal fibre intake. The incidence of T2DM was assessed in nine studies and changes in weight gain in two studies. The prospective studies consistently showed a reduced risk for high intake of whole grain foods (27% to 30%) or cereal fibre (28% to 37%) on the development of T2DM.
The evidence from only prospective cohort trials is considered to be too weak to be able to draw a definite conclusion about the preventive effect of whole grain foods on the development of T2DM. Properly designed long-term randomised controlled trials are needed. To facilitate this, further mechanistic research should focus on finding a set of relevant intermediate endpoints for T2DM and on identifying genetic subgroups of the population at risk that are most susceptible to dietary intervention.
"Heterogeneity of studies can be a reason not to perform a meta-analysis. For example, a systematic review of whole grain foods and T2D that had intended to complete a meta-analysis concluded a qualitative synthesis was more appropriate for the data . Other investigators have determined that a meta-analysis of this topic was informative [59,60]. "
[Show abstract][Hide abstract] ABSTRACT: Background
Assessment of design heterogeneity conducted prior to meta-analysis is infrequently reported; it is often presented post hoc to explain statistical heterogeneity. However, design heterogeneity determines the mix of included studies and how they are analyzed in a meta-analysis, which in turn can importantly influence the results. The goal of this work is to introduce ways to improve the assessment and reporting of design heterogeneity prior to statistical summarization of epidemiologic studies.
In this paper, we use an assessment of sugar-sweetened beverages (SSB) and type 2 diabetes (T2D) as an example to show how a technique called ‘evidence mapping’ can be used to organize studies and evaluate design heterogeneity prior to meta-analysis.. Employing a systematic and reproducible approach, we evaluated the following elements across 11 selected cohort studies: variation in definitions of SSB, T2D, and co-variables, design features and population characteristics associated with specific definitions of SSB, and diversity in modeling strategies.
Evidence mapping strategies effectively organized complex data and clearly depicted design heterogeneity. For example, across 11 studies of SSB and T2D, 7 measured diet only once (with 7 to 16 years of disease follow-up), 5 included primarily low SSB consumers, and 3 defined the study variable (SSB) as consumption of either sugar or artificially-sweetened beverages. This exercise also identified diversity in analysis strategies, such as adjustment for 11 to 17 co-variables and a large degree of fluctuation in SSB-T2D risk estimates depending on variables selected for multivariable models (2 to 95% change in the risk estimate from the age-adjusted model).
Meta-analysis seeks to understand heterogeneity in addition to computing a summary risk estimate. This strategy effectively documents design heterogeneity, thus improving the practice of meta-analysis by aiding in: 1) protocol and analysis planning, 2) transparent reporting of differences in study designs, and 3) interpretation of pooled estimates. We recommend expanding the practice of meta-analysis reporting to include a table that summarizes design heterogeneity. This would provide readers with more evidence to interpret the summary risk estimates.
"We found that one-year death in these patients was dependent on the consumption of some nutrient components such as saturated fatty acids and cholesterol. Epidemiological studies strongly support the suggestion that low intakes of cholesterol and free fatty acids prevent the development of type II diabetes mellitus and people who consume foods with the lowest levels of these nutritional agents are less likely to develop diabetes and its-related complications than higher level consumers.19,20 The effect of low-fat diets in the prevention of CAD has also been demonstrated. "
[Show abstract][Hide abstract] ABSTRACT: The impact of different nutritional regimens on long-term prognosis and outcome in diabetic patients with coronary artery disease (CAD) has been questioned. Therefore, the objective of the present study was to determine the effects of different nutritional components of Mediterranean regimen on long-term cardiovascular events in diabetic patients with CAD in the Iranian population.
In a prospective cohort study, we recruited 233 consecutive patients with the diagnosis of type 2 diabetes mellitus and with at least 6 months of documented CAD. Nutritional assessment was obtained by a validated semi-quantitative food frequency questionnaire (FFQ) and the diet score was calculated on the basis of the Mediterranean diet quality index (Med-DQI). For Assessing long-term CAD prognosis, the patients were followed by telephone for one year. The study endpoint was long-term major adverse cardiac and cerebrovascular event (MACCE).
Death was observed in 19 patients (8.2%) during the one-year follow-up. Two patients (0.9%) suffered non-fatal myocardial infarction and 14 (6.0%) needed revascularization within 1 year after discharge from hospital. Overall MACCE within one year in the study population was 12.4%. There were significant differences between number of deaths and dietary scores of saturated fatty acid, cholesterol, meats, fish, and fruit and vegetables (P < 0.05). Moreover, significant differences were found between MACCE rate and dietary scores of saturated fatty acid, cholesterol, and fruit and vegetables (P < 0.05). Using multivariate logistic regression models, Mediterranean dietary regimen could effectively predict long-term death as well as MACCE adjusted for gender and age variables.
Mediterranean dietary regimens, including low level of cholesterol and saturated fatty acid, can effectively improve long-term outcome including death and MACCE in diabetic patients with CAD.
"Dietary patterns featuring wholegrain cereals are associated with reduced risk of T2D [7-10]. Systematic reviews and meta-analyses of large, prospective studies consistently demonstrate that frequent consumption of wholegrain foods improves metabolic homeostasis and delays or prevents the development of T2D and its complications in a variety of cohorts, albeit mostly of European ancestry [11-18]. Two to three serves daily of wholegrain foods reduced the risk of T2D by 20-30% compared to about 1 serve a week [12,13,15,18]. "
[Show abstract][Hide abstract] ABSTRACT: Diets high in wholegrains are associated with a 20-30% reduction in risk of developing type-2 diabetes (T2D), which is attributed to a variety of wholegrain components, notably dietary fibre, vitamins, minerals and phytochemicals. Most phytochemicals function as antioxidants in vitro and have the potential to mitigate oxidative stress and inflammation which are implicated in the pathogenesis of T2D. In this review we compare the content and bioavailability of phytochemicals in wheat, barley, rice, rye and oat varieties and critically evaluate the evidence for wholegrain cereals and cereal fractions increasing plasma phytochemical concentrations and reducing oxidative stress and inflammation in humans. Phytochemical content varies considerably within and among the major cereal varieties. Differences in genetics and agro-climatic conditions explain much of the variation. For a number of the major phytochemicals, such as phenolics and flavanoids, their content in grains may be high but because these compounds are tightly bound to the cell wall matrix, their bioavailability is often limited. Clinical trials show that postprandial plasma phenolic concentrations are increased after consumption of wholegrain wheat or wheat bran however the magnitude of the response is usually modest and transient. Whether this is sufficient to bolster antioxidant defences and translates into improved health outcomes is still uncertain. Increased phytochemical bioavailability may be achieved through bio-processing of grains but the improvements so far are small and have not yet led to changes in clinical or physiological markers associated with reduced risk of T2D. Furthermore, the effect of wholegrain cereals and cereal fractions on biomarkers of oxidative stress or strengthening antioxidant defence in healthy individuals is generally small or nonexistent, whereas biomarkers of systemic inflammation tend to be reduced in people consuming high intakes of wholegrains. Future dietary intervention studies seeking to establish a direct role of phytochemicals in mediating the metabolic health benefits of wholegrains, and their potential for mitigating disease progression, should consider using varieties that deliver the highest possible levels of bioavailable phytochemicals in the context of whole foods and diets. Both postprandial and prolonged responses in systemic phytochemical concentrations and markers of inflammation and oxidative stress should be assessed along with changes related to health outcomes in healthy individuals as well as those with metabolic disease.
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