Following a Mediterranean diet, with or without added exercise and physical activity, can lower the risk of a heart attack, stroke or early death for people at risk of cardiovascular disease, found a global review of evidence by experts from six countries.
A diet rich in olive oil, nuts, seafood, whole grains and vegetables has previously been linked to numerous benefits, and its effectiveness in helping healthy people to live longer is well known.
However, until now there’s been limited evidence of how it might help those at increased risk of cardiovascular disease: this includes people with obesity, type 2 diabetes, high blood pressure or high cholesterol, and those who are physically inactive, smoke or consume harmful levels of alcohol.
Currently, guidelines recommend various diets for those at higher risk of heart issues, but typically, they rely on low-certainty evidence from non-randomised studies.
Now, this large study – the first of its kind in the world – analysing 40 randomised controlled trials involving more than 35 000 people, has provided robust evidence, reports The Guardian.
Mediterranean and low-fat diets reduce the likelihood of death and heart attack in people at heightened risk of cardiovascular disease, according to the first comparative review of seven programmes published in The BMJ.
“Moderate-certainty evidence shows that programmes promoting Mediterranean and low-fat diets, with or without physical activity or other interventions, reduce all-cause mortality and non-fatal myocardial infarction (heart attacks) in patients with increased cardiovascular risk,” the study’s authors wrote. “Mediterranean programmes are also likely to reduce stroke risk.”
The 40 trials involving the nearly 36 000 participants – who were followed for an average of three years across seven diet programmes – were reviewed by researchers from the US, Canada, China, Spain, Colombia and Brazil.
The seven diets were: Mediterranean, low fat, very low fat, modified fat, combined low fat and low sodium, Ornish (a vegetarian diet, low in fat and refined sugar), and Pritikin (a low-fat, high-fibre diet, limiting processed food and red meat).
Based on moderate-certainty evidence, Mediterranean diet programmes were better than minimal intervention at preventing all-cause mortality, non-fatal heart attack and stroke in people at risk of cardiovascular disease.
Low-fat programmes were also superior to minimal intervention, with moderate certainty, for prevention of all-cause mortality and non-fatal heart attack.
The five other dietary programmes generally had little or no benefit compared with minimal intervention, typically based on low- to moderate-certainty evidence.
The researchers acknowledged several limitations to their work, such as being unable to measure adherence to diet programmes and the possibility that some of the benefits may have been due to other elements within the programmes, such as drug treatments and support to stop smoking.
Nevertheless, The BMJ said it was a comprehensive review.
Study details
Comparison of seven popular structured dietary programmes and risk of mortality and major cardiovascular events in patients at increased cardiovascular risk: systematic review and network meta-analysis
Giorgio Karam, Arnav Agarwal, Behnam Sadeghirad, Gordon Guyatt, Bradley Johnston, et al.
Published in The BMJ on 29 March 2023
Abstract
Objective To determine the relative efficacy of structured named diet and health behaviour programmes (dietary programmes) for prevention of mortality and major cardiovascular events in patients at increased risk of cardiovascular disease.
Design Systematic review and network meta-analysis of randomised controlled trials.
Data sources AMED (Allied and Complementary Medicine Database), CENTRAL (Cochrane Central Register of Controlled Trials), Embase, Medline, CINAHL (Cumulative Index to Nursing and Allied Health Literature), and ClinicalTrials.gov were searched up to September 2021.
Study selection Randomised trials of patients at increased risk of cardiovascular disease that compared dietary programmes with minimal intervention (eg, healthy diet brochure) or alternative programmes with at least nine months of follow-up and reporting on mortality or major cardiovascular events (such as stroke or non-fatal myocardial infarction). In addition to dietary intervention, dietary programmes could also include exercise, behavioural support, and other secondary interventions such as drug treatment.
Outcomes and measures
All cause mortality, cardiovascular mortality, and individual cardiovascular events (stroke, non-fatal myocardial infarction, and unplanned cardiovascular interventions).
Review methods
Pairs of reviewers independently extracted data and assessed risk of bias. A random effects network meta-analysis was performed using a frequentist approach and grading of recommendations assessment, development and evaluation (GRADE) methods to determine the certainty of evidence for each outcome.
Results
Forty eligible trials were identified with 35 548 participants across seven named dietary programmes (low fat, 18 studies; Mediterranean, 12; very low fat, 6; modified fat, 4; combined low fat and low sodium, 3; Ornish, 3; Pritikin, 1). At last reported follow-up, based on moderate certainty evidence, Mediterranean dietary programmes proved superior to minimal intervention for the prevention of all cause mortality (odds ratio 0.72, 95% confidence interval 0.56 to 0.92; patients at intermediate risk: risk difference 17 fewer per 1000 followed over five years), cardiovascular mortality (0.55, 0.39 to 0.78; 13 fewer per 1000), stroke (0.65, 0.46 to 0.93; 7 fewer per 1000), and non-fatal myocardial infarction (0.48, 0.36 to 0.65; 17 fewer per 1000). Based on moderate certainty evidence, low fat programmes proved superior to minimal intervention for prevention of all cause mortality (0.84, 0.74 to 0.95; 9 fewer per 1000) and non-fatal myocardial infarction (0.77, 0.61 to 0.96; 7 fewer per 1000). The absolute effects for both dietary programmes were more pronounced for patients at high risk. There were no convincing differences between Mediterranean and low fat programmes for mortality or non-fatal myocardial infarction. The five remaining dietary programmes generally had little or no benefit compared with minimal intervention typically based on low to moderate certainty evidence.
Conclusions
Moderate certainty evidence shows that programmes promoting Mediterranean and low fat diets, with or without physical activity or other interventions, reduce all cause mortality and non-fatal myocardial infarction in patients with increased cardiovascular risk. Mediterranean programmes are also likely to reduce stroke risk. Generally, other named dietary programmes were not superior to minimal intervention.
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