The objective of the study was to determine the relative efficacy of structured named diet and health behavior programs (dietary programs) for prevention of mortality and major cardiovascular events in patients at increased risk of cardiovascular disease. The results of this systematic review and network meta-analysis showed that the Mediterranean diet reduces all cause mortality in patients with increased cardiovascular risk.
Dietary guidelines recommend various dietary programs for patients with increased cardiovascular risk, but they may be based on low certainty evidence, such as non-randomized studies. Numerous diets, with or without exercise and behavioral support (known as dietary programs), reduce major cardiovascular events. These diets include diets low in total or saturated fats (e.g., the National Cholesterol Education Program diets), Mediterranean style diets, and the Dietary Approaches to Stop Hypertension (DASH) diet.
Systematic reviews of randomized trials with mortality and major cardiovascular outcomes have reported benefits of dietary programs, but have not used network meta-analysis to provide absolute estimates and certainty of estimates for patients at intermediate and high risk. Network meta-analytic method enables the use of direct evidence (head to-head active interventions) and indirect evidence (intervention versus non-active control) to compare interventions that have not been directly compared, which may lead to more accurate estimates.
The Mediterranean diet is a century-old approach to meals, traditional to the countries bordering the Mediterranean Sea. The bulk of the diet consists of colorful fruits and vegetables, plus whole grains, legumes, nuts and seeds, fish and seafood, with olive oil and perhaps a glass of red wine. There is no butter, no refined grains (like white bread, pasta, and rice), and very little red or processed meat (like bacon). In a Mediterranean-style diet every meal should have vegetables and fruits as a base. Any grains should be whole grains, like quinoa, brown rice, corn, farro, or whole wheat. Legumes are an excellent source of plant protein, such as lentils, garbanzo, kidney, cannellini, or black beans. Nuts and seeds contain protein and healthy fats, and olive oil provides even more healthy fats. Including fish and seafood is traditional.
About the study
This network meta-analysis compared the effects of different dietary programs on clinical outcomes, such as mortality and cardiovascular events, using GRADE (Grading of Recommendations Assessment, Development and Evaluation) methods. The objective of the study was to determine the relative efficacy of structured named diet and health behavior programs (dietary programs) for prevention of mortality and major cardiovascular events in patients at increased risk of cardiovascular disease.
The authors searched five databases: AMED (Allied and Complementary
Medicine Database), Cochrane Central Register of Controlled Trials (CENTRAL), EMBASE, Medline, and CINAHL (Cumulative Index to Nursing and Allied Health Literature) from inception to September 2021, and ClinicalTrials.gov for unpublished and ongoing trials. 40 eligible trials were identified with 35 548 participants across seven named dietary programs (low fat, 18 studies; Mediterranean, 12; very low fat, 6; modified fat, 4; combined low fat and low sodium, 3; Ornish, 3; Pritikin, 1).
The researchers included randomized trials of adults at increased risk of cardiovascular disease that compared at least one structured dietary program with minimal intervention, or with other cardiovascular risk reduction interventions (including other dietary programs). Eligible trials enrolled patients with two or more established risk factors for cardiovascular disease (eg, hypertension, dyslipidemia, obesity, diabetes mellitus), or established cardiovascular disease (history of coronary artery disease, myocardial infarction, stroke, or peripheral artery disease).
In addition to the diet intervention, structured dietary programs could include non-dietary interventions, such as exercise, or psychosocial or behavioral support. Smoking cessation interventions and drug treatments were also permitted, but were considered co-interventions. The authors have divided low fat diet category to low fat (20-30% calories from fat) and very low fat (≤20% calories from fat) to distinguish standard low fat dietary programs from programs with a more intense fat reduction goal. They also added a modified fat category (not a reduction in total fat intake, but an increase in polyunsaturated fats).
The results of this study showed that Mediterranean and low fat diets reduce all cause mortality and non-fatal myocardial infarction in patients with increased cardiovascular risk. A Mediterranean diet was not convincingly superior to a low fat diet for these results. The absolute effects of both dietary programs were more pronounced in high-risk patients.
The Mediterranean dietary programs were superior to minimal intervention for the prevention of all cause mortality, cardiovascular mortality, stroke, and non-fatal myocardial infarction in patients with increased cardiovascular risk. Low fat dietary programs were also superior to minimal intervention with low to moderate certainty for prevention of all cause mortality and non-fatal myocardial infarction.
There were no convincing differences between Mediterranean and low fat programs for mortality or non-fatal myocardial infarction. The five remaining dietary programs generally had little or no benefit compared to a minimal intervention typically based on low to moderate certainty evidence.
This article was published in the scientific journal British Medical Journal. Karam G et al. Comparison of seven popular structured dietary programs and risk of mortality and major cardiovascular events in patients at increased cardiovascular risk: systematic review and network meta-analysis. BMJ 2023;380:e072003 http://dx.doi.org/10.1136/bmj-2022-072003
It should be noted here that a large population-based prospective cohort study showed that higher adherence to the Mediterranean diet was associated with a lower risk for all-cause dementia. https://discovermednews.com/higher-adherence-to-the-mediterranean-diet-is-associated-with-a-lower-risk-of-dementia/?preview=true
Additionally, a recent study has found that women with the highest adherence to the Mediterranean diet before conception have the lowest risk of developing adverse pregnancy outcomes, in particular preeclampsia or eclampsia and gestational diabetes. https://discovermednews.com/the-mediterranean-diet-is-associated-with-a-lower-risk-of-adverse-pregnancy-outcomes/