According to the World Health Organization (WHO), cardiovascular diseases (CVDs) are the leading cause of death globally.
In 2019, an estimated 17.9 million deaths occurred due to CVDs, representing 32% of all deaths worldwide. People who are at risk of CVDs often receive dietary recommendations from healthcare professionals.
However, it can be challenging to determine which dietary programs are effective in reducing the risk of CVDs.
To address this issue, researchers at the University of Manitoba conducted a systematic review and meta-analysis of published studies to compare the effectiveness of different dietary programs in preventing heart attacks and strokes and all-cause death.
The study is the first comparative review based on randomized trials of seven popular dietary programs, including low-fat, Mediterranean, very low-fat, modified fat, combined low-fat and low-sodium, Ornish, and Pritikin diets.
The researchers searched several databases for randomized trials looking at the impact of dietary programs on preventing death and major cardiovascular events in patients at increased risk of cardiovascular disease.
Forty eligible trials were identified involving 35,548 participants who were followed for an average of three years across seven named dietary programs.
The trials included patients with different levels of cardiovascular risk, from those with no history of cardiovascular disease to those with existing cardiovascular disease.
The dietary programs were provided with or without exercise and other health behavior support.
The trials compared the effectiveness of the different dietary programs with minimal intervention, such as the usual diet or brief dietary advice from a health professional.
The study found that Mediterranean and low-fat dietary programs reduce the likelihood of death and heart attack in patients at heightened risk of cardiovascular disease.
The researchers found that Mediterranean dietary programs were better than minimal intervention at preventing all-cause mortality, non-fatal heart attack, and stroke for patients at intermediate risk of heart disease.
Low-fat programs were also superior to minimal intervention for the prevention of all-cause mortality and non-fatal heart attack.
When compared with one another, there were no convincing differences between Mediterranean and low-fat programs for mortality or non-fatal heart attack.
The absolute effects for both dietary programs were more pronounced for patients at high risk of cardiovascular disease.
For example, those following the Mediterranean diet had 36 fewer all-cause deaths per 1000 and 39 fewer cardiovascular deaths per 1000 over five years.
The study also found that other named dietary programs were generally not superior to minimal intervention, typically based on low to moderate certainty evidence.
However, the researchers acknowledged several limitations, such as being unable to measure adherence to dietary programs and the possibility that some of the benefits may have been due to other elements within the programs like drug treatment and support to stop smoking.
Overall, the study provides evidence that Mediterranean and low-fat dietary programs can reduce the risk of mortality and non-fatal myocardial infarction in people at increased cardiovascular risk.
The Mediterranean diet emphasizes the consumption of fruits, vegetables, whole grains, legumes, and nuts while limiting the intake of red meat, processed foods, and unhealthy fats.
The low-fat diet aims to reduce total and saturated fat intake while increasing the consumption of fruits, vegetables, whole grains, and lean protein sources.
The study has important implications for healthcare professionals and patients at risk of cardiovascular disease.
Current guidelines recommend various dietary programs for patients at increased cardiovascular risk, but they have typically relied on low-certainty evidence from non-randomized studies.
This study provides stronger evidence based on randomized controlled trials that can help inform dietary recommendations for patients.
While the study has some limitations, it is a comprehensive review based on a thorough literature search, rigorous assessment of study bias, and adherence to recognized GRADE methods to assess the certainty of estimates.
The study underscores the importance of adopting healthy eating habits to reduce heart disease risk.
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The study was conducted by Giorgio Karam et al and published in The BMJ.
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