Understanding the Impact of Mediterranean Diet and Processed Foods on Heart Health

A notable study, the Primary Prevention of Cardiovascular Disease with a Mediterranean Diet, published in the New England Journal of Medicine, included 7,447 subjects with cardiovascular risk factors. Participants were divided into three groups: one following a Mediterranean diet with extra-virgin olive oil, another with extra nuts, and a control group that maintained their usual diet with some fat intake guidance. The Mediterranean diet focuses on vegetables, fruits, nuts, fish, and olive oil, while limiting sweets and red meats.

After an average follow-up of 4.8 years, the study recorded 96, 83, and 109 cardiovascular events among the three groups. This led to an HR of 0.7, which some media outlets translated to mean that following a Mediterranean diet could cut heart disease risk by 30 percent. This interpretation is misleading. An HR represents the likelihood of an event occurring in one group compared to another. An HR of 0.7 indicates that the treatment group experiences 70 percent of the event rate seen in the control group, but it does not directly relate to the number of events avoided.

When examining annual events, it was found that for every 1,000 participants on the Mediterranean diet, there were eight cardiovascular events, while the control group had 11. Therefore, only three fewer events occur each year per 1,000 individuals following the Mediterranean diet, suggesting a 1.5 percent chance of avoiding an event over five years, which is significantly less impressive than the 30 percent figure.

The potential benefit for large populations remains considerable: for one million individuals adopting this diet, an estimated 15,000 events could be avoided over five years. However, the reliability of the HR is also crucial, as indicated by the confidence interval which, in this study, ranged from 0.54 to 0.92, revealing variability in the data that raises concerns about its robustness.

In a separate study titled Ultra-processed food intake and risk of cardiovascular disease, published in the British Medical Journal, French researchers tracked over 100,000 participants’ diets over five years. They classified food items based on the NOVA system and determined that each 10 percent increase in ultra-processed food consumption correlated with a 12 percent higher risk of cardiovascular disease. Yet, breaking down the numbers shows that among 1,000 people consuming a low ultra-processed food diet, approximately five would have cardiovascular events, and high consumers would statistically increase their events by 0.6 annually. Thus, to prevent one cardiovascular incident per year, roughly 2,000 people would need to limit their ultra-processed food intake.

The confidence interval for this study was also wide, ranging from 1.05 to 1.20, implying the actual increase in risk could fluctuate between 5 percent and 20 percent. Such variability is common in nutritional studies, as many confounding factors can affect outcomes.

Despite these complexities, following a Mediterranean diet and reducing ultra-processed food intake can still be beneficial for individual health and public health at large. For example, in Canada, approximately 12 million adults have multiple risk factors for heart disease, meaning even a small percentage of improvement could lead to significant reductions in cardiovascular events.

In summary, while the individual benefits might seem modest, they could translate into substantial public health outcomes. Individuals are encouraged to embrace the Mediterranean diet's principles by incorporating more fruits, vegetables, nuts, and extra virgin olive oil, while reducing the consumption of ultra-processed foods.