Umbrella Review of the DASH Dietary Pattern and Cardiometabolic Risk

The European Association for the Study of Diabetes (EASD) guidelines have not made any specific recommendations regarding the Dietary Approaches to Stop Hypertension (DASH) diet, a dietary pattern that emphasizes fruits and vegetables, low-fat or non-fat dairy, limiting saturated fat intake and usually also recommends limiting sodium intake. To update the recommendations, the Diabetes and Nutrition Study Group (DNSG) of the EASD commissioned an umbrella review of systematic reviews and meta-analyses using the Grading of Recommendations Assessment, Development, and Evaluation (GRADE) approach to summarize the available evidence from recent systematic reviews and meta-analyses of prospective cohort studies and randomized and non-randomized controlled trials of the relationship between the DASH dietary pattern and cardiometabolic risk.

Background: The DASH Dietary Pattern, which emphasizes intake of fruits and vegetables, low-fat or non-fat dairy, nuts, and legumes and limits saturated fat and red meat intake, is associated with reduced cardiovascular disease and diabetes risk in prospective cohort studies and has been shown to lower blood pressure and other intermediate cardiometabolic risk factors in randomized controlled trials. Despite the endorsement of the DASH Dietary Pattern by major international diabetes and cardiovascular guidelines, the European Association for the Study of Diabetes (EASD) guidelines for nutrition therapy have not made any specific recommendations for the DASH dietary pattern. The present umbrella review using the Grading of Recommendations Assessment, Development, and Evaluation (GRADE) approach was commissioned by the Diabetes and Nutrition Study Group (DNSG) of the EASD to summarize the available evidence from recent systematic reviews and meta-analyses of prospective cohort studies and randomized and non-randomized controlled trials of the relationship between the DASH dietary pattern and cardiometabolic risk.

Need for proposed research: Public health policy and clinical practice guidelines are established with the use of systematic reviews and meta-analyses of randomized and non-randomized controlled trials and prospective cohort studies, which are regarded as the highest levels of evidence. As dietary guidelines and public health policy have shifted toward food and dietary-pattern based recommendations, there is a need to summarize the evidence from systematic reviews and meta-analyses assessing the effect of the DASH dietary pattern trials on cardiometabolic risk factors.

Objective: The investigators will conduct an umbrella review of systematic reviews and meta-analyses using GRADE to summarize the relation of the DASH dietary pattern with incident cardiometabolic disease outcomes in prospective cohort studies and the effect the DASH dietary pattern on intermediate cardiometabolic risk factors in randomzied and non-randomized controlled trials.

Design: The umbrella review will be conducted according to the principals of the Cochrane Handbook for Systematic Reviews of Interventions for the controlled clinical trials and the GRADE handbook with reporting according to the Meta-analysis Of Observational Studies in Epidemiology (MOOSE) guidelines for prospective cohort studies and the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) for controlled trials.

Data sources: MEDLINE and EMBASE will be searched using appropriate search terms. Authors will be contacted for applicable missing data.

Study selection: The investigators will include the most recent and/or comprehensive systematic reviews and meta-analyses assessing the relation of the DASH dietary pattern with incident cardiometabolic diseases (CVD, coronary heart disease (CHD), stroke, diabetes) in prospective cohort studies and the effect on intermediate cardiometabolic risk factors (blood pressure, blood lipids, glycemic control, adiposity, and inflammation) in randomized and non-randomized controlled trials. If the search did not identify an existing systematic review and meta-analysis on any of our pre-specified outcomes (please refer to Outcomes), we then conducted a systematic search for that outcome and performed a meta-analysis on all studies retrieved which assess the effect in controlled trials (or association for prospective cohorts) of the DASH diet compared to a control diet on that outcome.

Data extraction: Two or more investigators will independently extract relevant data and assess risk of bias of the individual studies using the Newcastle-Ottawa Scale for observational studies and the Cochrane Risk of Bias Tool for controlled clinical trials. All disagreements will be resolved by consensus.

Outcomes: The primary outcome will be incident cardiovascular disease (CVD) in the prospective cohort studies and systolic blood pressure in the randomized and non-randomized controlled trials. Secondary outcomes will include incident coronary heart disease (CHD), stroke, and diabetes in the prospective cohort studies and diastolic blood pressure, blood lipids (total-C, LDL-C, HDL-C, and triglycerides), glycemic control (HbA1c, fasting blood glucose, fasting blood insulin, homeostasis model assessment of insulin resistance \[HOMA-IR\]), adiposity (body weight), and inflammation (C-reactive protein) in controlled trials.

Evidence Assessment: The certainty of the evidence for each outcome will be assessed using the Grading of Recommendations Assessment, Development and Evaluation (GRADE).

Knowledge translation plan: The results will be disseminated through interactive presentations at local, national, and international scientific meetings and publication in high impact factor journals. Target audiences will include the public health and scientific communities with interest in nutrition, diabetes, obesity, and cardiovascular disease. Feedback will be incorporated and used to improve the public health message and key areas for future research will be defined. Applicant/Co-applicant Decision Makers will network among opinion leaders to increase awareness and participate directly as committee members in the development of future guidelines.

Significance: The proposed project will aid in knowledge translation related to the role of the DASH dietary pattern in cardiometabolic risk, strengthening the evidence-base for guidelines and improving health outcomes by educating healthcare providers and patients, stimulating industry innovation, and guiding future research design.

Eligibility Criteria:
Inclusion Criteria:

* Systematic reviews and meta-analyses of prospective cohorts or controlled clinical trials
* Assessment of the DASH dietary pattern
* Viable outcome data with ≥ 1 outcome of interest

Exclusion Criteria:

* Non-systematic review and meta-analysis publications
* Non-human studies
* No assessment of the exposure of the DASH dietary pattern
* No viable outcome data