More than 18,000 people living in the Molise region of southern Italy participated in the study
A Mediterranean diet emphasizes eating plant-based foods, fish and poultry while limiting red meat
The Mediterranean diet can reduce the risk of cardiovascular disease, yet only people with higher incomes or more education, or a combination of the two, experience this benefit, found a study published Monday in the International Journal of Epidemiology.
The Mediterranean diet emphasizes eating plant-based foods, including vegetables, nuts, fruits and whole grains, in addition to fish and poultry. The diet also recommends that you limit red meat, replace butter with olive oil, and exercise. Red wine in moderation is optional on the diet, which past scientific research proves to be heart-healthy.
Marialaura Bonaccio, lead author of the new study and a researcher at IRCCS Istituto Neurologico Mediterraneo Neuromed, an Italian Clinical Research Institute, said in an email that this same problem – in which people from different income levels get different results from the same diet – may also be true for other diets.
The reason? Diets “focus on quantity, rather than on quality” of the food, she said.
Bonaccio and her co-authors randomly recruited over 18,000 people living in the Molise region of southern Italy between March 2005 and April 2010. The Pfizer Foundation, which helped fund enrollment costs, did not influence the analysis or interpretation of results, Bonaccio noted.
She and her team calculated total physical activity, body mass index (BMI), smoking status and health history, including cardiovascular disease, diabetes and cancer. The data available for each participant also included education, household income and marital status.
Using the Mediterranean Diet Score, Bonaccio and her colleagues assessed participants’ food intake, examining the variety of fruits and vegetables, meat and fish consumed. They scored participants’ cooking methods, detailing whether they’re using healthy methods such as boiling and stewing or less healthy methods such as frying, roasting and grilling. Vegetables were categorized as organic or not, bread as whole-grain or not.
Over an average followup period of about four years, participants experienced a total of 5,256 cardiovascular disease events, including incidents of heart failure, diagnoses of coronary heart disease (a buildup of plaque in the arteries) and strokes.
Analyzing the data, the researchers found that a Mediterranean diet effectively reduced cardiovascular disease risk, but only among a select group of participants: those with higher income or more education.
“We found heart advantages were limited to high socioeconomic status groups, even if groups showed the same adherence to the Mediterranean diet,” Bonaccio wrote. No benefits occurred for participants in the low income and low education group.
Differences in food quality
Surprised by this result, the researchers dug into the data more deeply and unearthed a possible reason for the difference: The same Mediterranean diet adherence score still included slight differences in food consumption.
“For example, as compared to less advantaged counterparts, people with high socioeconomic status tended to consume fish more frequently,” Bonaccio wrote. She added that, beyond diet adherence, participants in the most advantaged category reported a higher quality diet, which included higher consumption of organic products and whole grain foods.
“Let’s give that two persons follow the same diet, that is equal amounts of vegetables, fruits, fish, olive oil etc. every day so that they report the same adherence score to Mediterranean diet,” Bonaccio said. “It might be that, beyond quantity, differences in quality may exist. For example, in olive oil.”
She said it’s unlikely that a bottle of extra virgin olive oil with a price tag of 2 to 3 euros has the same nutritional properties as one costing 10 euros. Given that it is reasonable to assume higher-income participants are more likely to buy the 10-euro bottle compared with lower-income participants, “our hypothesis is that differences in the price m