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|Issue 104||January 2016|
The report is a product of the VA/HSR&D Evidence Synthesis Program.
Benefits and Harms of the Mediterranean Diet Compared to Other Diets
A large number of studies have investigated the association between diet and mortality and morbidity. Of particular interest is the Mediterranean diet, which is characterized by:
Epidemiologic studies have shown that the incidence of cardiovascular disease in populations that consume such diets is lower than in populations that consume a more typical "Western" diet that is rich in red meat, dairy products, processed and artificially sweetened foods, and salt, with minimal intake of fruits, vegetables, fish, legumes, and whole grains. Based on these studies, several randomized controlled trials (RCTs) were conducted to test the hypothesis that adopting a Mediterranean diet in adulthood reduces chronic disease burden (e.g., cardiovascular disease, cancer, diabetes, hypertension, cognitive impairment, and kidney disease) and/or all-cause mortality. These trials included populations from a variety of geographical locations, and with a spectrum of demographic and clinical characteristics.
VA's Evidence-based Synthesis Program (ESP), in conjunction with the Office of Quality and Performance – and in response to a request from VA's National Center for Health Promotion and Disease Prevention (NCP) and Primary Care Services (PCS) – commissioned this evidence report to update prior reviews, and to specifically assess the implications for the treatment and prevention of common chronic conditions in the Veteran population. Conducted by the ESP Center located at the Minneapolis VA Medical Center, investigators reviewed the literature from 1990 through August 2015 and identified 55 published studies that met their inclusion criteria.
Primary Prevention: Cardiovascular Disease and Type 2 Diabetes
A second primary prevention study – the Women's Health Initiative Dietary Modification (WHI-DM) trial – found no difference in the incidence of major cardiovascular events or diabetes between its two diet groups. Although this study met the definition of a Mediterranean diet used for this evidence report, it only included 2 of 7 Mediterranean diet components (fruits/vegetables and grains), and its primary goal was to lower total fat intake. Therefore, report investigators did not consider this intervention a true Mediterranean diet.
Secondary Prevention: Cardiovascular Disease and Type 2 Diabetes
Primary Prevention: Cancer
Secondary Prevention: Cancer
Investigators identified a single primary prevention trial which found that consumption of a Mediterranean diet was associated with a significant reduction in major cardiac events, new-onset type 2 diabetes, and breast cancer incidence. For secondary prevention, data from two trials indicate that assignment to a Mediterranean diet reduces incidence of myocardial infarction, but not other cardiovascular outcomes. Cohort studies indicate that conformity to a Mediterranean diet pattern is associated with significant reduction in total cancer incidence, total cancer mortality, and colorectal cancer incidence. However, these associations have not been confirmed in RCTs. The available data on other outcomes such as cognitive impairment and rheumatoid arthritis were limited. The available data on dietary adherence suggest that sustained increases in the consumption of fruits, vegetables, and grains can be achieved with labor-intensive behavioral interventions in select populations.
A major gap in the research is the absence of large-scale clinical outcomes trials of a Mediterranean diet in North American populations, both in primary and secondary prevention populations. Such trials are important to confirm results of the few trials performed abroad and to determine the acceptability of the Mediterranean diet to the American public. In addition, the following areas represent important avenues for future research:
Implications for Policy and Practice
Though the Mediterranean Diet may show some promise as a dietary approach for preventing overall mortality, cardiovascular disease, and some cancers, the quality of available evidence for the Mediterranean diet's effects on these outcomes is low or insufficient, and is especially lacking in North American and U.S. Veteran populations. Moreover, adherence to a Mediterranean diet is challenging outside the context of an intervention trial that offers considerable behavioral intervention. Therefore, the results of this review will not change the core content of NCP's "Eat Wisely" Healthy Living message, which emphasizes eating a variety of foods, including vegetables, fruits, and whole grains and that already features nuts, fish, and foods low in saturated fats. These findings also will not significantly alter the dietary recommendations featured in the MOVE! Weight Management Program, which are aligned with the 2014 VA/DoD Clinical Practice Guideline (CPG) for Screening and Management of Obesity. This CPG recommends offering any diet that produces a caloric deficit and has evidence for weight loss efficacy and safety, and also stresses that the focus should be on adherence to a diet that is individualized for medical and metabolic conditions and ease of long-term maintenance and adherence. NCP also concurs with the Report's recommendations regarding the need for supporting research that addresses current gaps in our understanding.
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ESP is currently soliciting review topics from the broader VA community. Nominations will be accepted electronically using the online Topic Submission Form. If your topic is selected for a synthesis, you will be contacted by an ESP Center to refine the questions and determine a timeline for the report.
This Management e-Brief is provided to inform you about recent HSR&D findings that may be of interest. The views expressed in this article are those of the authors and do not necessarily reflect the position or policy of the Department of Veterans Affairs. If you have any questions or comments about this Brief, please email CIDER. The Center for Information Dissemination and Education Resources (CIDER) is a VA HSR&D Resource Center charged with disseminating important HSR&D findings and information to policy makers, managers, clinicians, and researchers working to improve the health and care of Veterans.
This report is a product of VA/HSR&D's Quality Enhancement Research Initiative's (QUERI) Evidence-Based Synthesis Program (ESP), which was established to provide timely and accurate synthesis of targeted healthcare topics of particular importance to VA managers and policymakers – and to disseminate these reports throughout VA.
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