Heart disease remains one of the leading causes of death worldwide, so for decades researchers have been trying to understand which dietary regimen offers the best protection. It is now known that diet directly affects heart health, but research is still ongoing to determine the most effective dietary pattern.
For many years, it has been believed that a low-fat diet is the ideal choice for cardiovascular health. On the other hand, the Mediterranean diet has been consistently praised for its benefits and is supported by numerous scientific studies.
A new study, published in the American Journal of Clinical Nutrition, directly compared the Mediterranean diet, the American Heart Association's dietary recommendations, and a low-fat diet to see which is associated with the lowest risk for heart disease.
How was the study conducted?
Researchers analyzed data from two of the largest and longest-running studies in the United States, which have tracked the eating habits, lifestyles and health status of tens of thousands of participants for years.
Instead of organizing a new clinical trial, they used a statistical method that simulates the results of a randomized study based on existing data.
Three food patterns were compared:
The Mediterranean diet, rich in olive oil, nuts, fish, vegetables and legumes.
The American Heart Association's dietary recommendations for 2020, which emphasize the consumption of fruits, vegetables, fish, and whole grains.
Low-fat diet, which limits fried foods, nuts, sweets, fatty fish, and the use of fats or oils in cooking and salads.
They then calculated how the risk of cardiovascular disease would change over a 20-year period if participants followed each of these dietary patterns closely.
However, the researchers emphasize that this was not a classic experiment where participants were randomly assigned to follow a particular diet. Therefore, the study shows a link between diet and disease risk, but cannot prove cause and effect.
What did the study reveal?
In people at high risk for heart disease, the results were quite significant.
After 20 years, the estimated risk of developing cardiovascular disease was:
35.9% for those following the low-fat diet;
28.2% for those following the Mediterranean diet;
31.2% for those who followed the American Heart Association recommendations.
Although the percentage differences may seem small, the researchers emphasize that they are clinically important.
The benefits weren't limited to a reduced risk of heart disease. The Mediterranean diet and the American Heart Association's dietary pattern were also associated with:
fewer cases of coronary disease;
fewer deaths from cardiovascular causes;
fewer deaths from all causes.
The only exception was stroke. The researchers found no clear evidence that any of the diets significantly reduced this risk, which may be related to the fact that strokes have different causes and are more complex.
When the general population was also analyzed, not just those at high risk, the benefits were somewhat smaller but still significant. This suggests that these dietary patterns may be beneficial for most people, with the greatest effects seen in those with more risk factors.
Study limitations
The authors acknowledge that the study has some limitations. The dietary data was based on self-reported data from participants, which may be inaccurate.
Also, the Mediterranean diet analyzed was not identical to the traditional version used in European studies, but a variation adapted to the lifestyle in the United States. For example, the researchers were unable to determine how much of the oil consumed was extra virgin olive oil and how much was regular olive oil.
Another limitation was the composition of the participants. The majority were white healthcare professionals, so the results may not apply equally to all population groups.
What does this mean in practice?
The main message is that simply reducing dietary fat does not appear to be the most effective strategy for protecting the heart. If fats are removed from the diet without replacing them with quality foods, the benefits may be limited.
Instead, the study supports a clear dietary pattern that includes:
lots of vegetables;
legumes;
fish;
whole grains;
nuts;
olive oil.
Replacing highly processed foods with simply "low-fat" products does not necessarily have the same effect. According to researchers, the quality of foods matters much more than reducing the amount of fat.
