Protocol: The effect of whole-grain dietary intake on non-communicable diseases: A systematic review, multivariate meta-analysis and dose-response of prospective cohorts, cross-sectional, case-control and intervention studies

Abstract

The proposed protocol is for a systematic review and meta-analysis on the effects of whole-grains (WG) on non-communicable diseases such as type 2 diabetes, cardiovascular disease, hypertension and obesity. The primary objectives is to explore the mechanisms of WG intake on multiple biomarkers of NCDs such as fasting glucose, fasting insulin and many others. The secondary objective will look at the dose-response relationship between these various mechanisms. The protocol outlines the motive and scope for the review, and methodology including the risk of bias, statistical analysis, screening and study criteria. The problem, condition or issueCereal grains contribute up to 300 million tons of world food supplies annually (eurostat, 2016). This has lead to a considerable interest in the effects of grains on human health, in particular whole-grains (WG). With non-communicable diseases (NCDs) such as diabetes, cardiovascular disease (CVD) and cancer accounting for 77% of burden of disease, WG consumption may mitigate the effects of NCDs (WHO, 2016). However, with a number of studies showing both a weak and strong association of WGs with NCDs, there is still speculation surrounding the effects of WG (McRae, 2016). Existing reviews mostly look at risk ratios not biomarkers of diseases. Although they provide valuable information, they often limit readers understanding, can be falsely interpreted, and do not provide information on underlying mechanisms (Knol et al, 2012). Most NCDs such as metabolic syndrome are diagnosed based on a cluster of biomarkers such as impaired glucose homeostasis, obesity and dyslipidemia (Alberti et al, 2005); Biomarkers may provide a more accurate way of assessing the effects of WG on NCDs.Another reason for varying results may also be attributed to the definition of WG which varies in a number of regions (Van der Kamp et al, 2014;Ross et al, 2017). The proposed review not only aims to elucidate the overall effect of WGs but encourage governments to adopt similar definitions and set new targets for WG consumption in order to improve population health. Whole-grain consumption and interventionsMost current interventions and cohorts consider WG intake as foods containing 25% or 30% WG weight depending on the definition adopted (Jacobs et al, 2007; Liu et al, 1999;Liu et al 2003). WGs are defined in all countries as containing all of the anatomical components of the grain, including the bran, germ and endosperm (Van der Kamp, 2014;Ross et al, 2017). Familiar grains such as rye, oats, wheat, barley, maize and rice are all considered WGs. While legumes and oilseeds are not (Van der Kamp, 2014). Over the years, WG consumption has been monitored in individuals with NCDs (e.g. diabetes) to assess the longitudinal effect of WG (Nimptsch et al, 2011). Similarly, there have been many interventions (e.g. random control trials) involving WG foods such as bread, cereals, or snacks in healthy individuals and individuals with NCDs (e.g. hypertension) (Kirwan et al, 2016). Cohorts attempt to measure ...