By Moira Johnson
For years, researchers have discussed the benefits of the Mediterranean Diet as a sustainable eating lifestyle. For those who may not be familiar with it, the Mediterranean Diet entails high consumption of fruits and vegetables, fish, nuts, olive oil, and whole grains, along with moderate amounts of dairy products and red wine. The Mediterranean Diet has been linked to many positive health outcomes including lower risk of heart disease and longer life expectancy.
However, recent research suggests that the benefits of the Mediterranean diet may not reach everyone equally. An Italian community survey of approximately 18,000 people followed over four years found that only individuals with an annual income of at least €40,000 (US$54,096) experienced the heart protective benefits of the Mediterranean diet. Below I share some of the possible reasons for this surprising finding as explained by the authors of the study, as well as my own insights.
- Food Quality – The researchers state that higher income study participants ate a wider variety of higher quality organic produce and whole grain foods, as well as more fish and less red meat. This suggests the possibility that people need to consume a more diverse array of the highest quality fresh fruits and vegetables to gain the most benefit from the Mediterranean diet.
- Cooking Methods – Lower-income study participants reported frying their foods more often, while those with higher incomes were more likely to report baking and boiling their foods. Frying foods can increase the level of trans-fats and calories (due to adding lots of oils), which would change the nutritional value of an otherwise healthy food.
Factors such as food quality and cooking methods are likely to account for at least some of the difference in who benefits from a Mediterranean diet. Frying oils, particularly those containing unsaturated fatty acids, can increase oxidation and reduce the healthy antioxidant content of that oil. However, two other major causes may also explain persistent income differences in the ability to benefit from healthy eating patterns.
- Food Access – In the US, 30 million people live in low-income areas with limited access to supermarkets. The lack of access to supermarkets leads people to rely heavily on convenience stores and gas stations for their food needs, which often results in the consumption of ultra-processed foods high in salt, fat, and sugar. The inability to access or afford fresh produce and lean meats disproportionately impacts low-income people, and affects their ability to adhere to the recommendations of heart healthy diets such as the Mediterranean diet.
- Stress of Low Status – A large body of research suggests that low-income people experience significantly more chronic stress in their daily lives than those from more privileged backgrounds. Stress is a known risk factor for cardiovascular disease (CVD). It is plausible that chronic stressors such as worries over job security, affordable housing and childcare, and interpersonal conflict may dampen the benefits of a heart-healthy diet even when it is accessible to lower-income people.
- Other Sources of Residual Confounding – In the fully adjusted model, the authors controlled for age, biological sex, energy intake, egg and potato consumption, education, household income, marital status, BMI, total physical activity, smoking, hypertension, and hypercholesterolaemia. This means that these variables are “held constant’ in the analysis. In other words, the effects of these variables will be accounted for, and they will not be the reason for why the association between the Mediterranean diet and health outcomes is distorted. However, it is possible that there are other factors that are associated with one’s eating habits that also affect cardiovascular disease risk, and this is what epidemiologists call confounding. If these confounding factors are different according to SES, then that could affect the results. The authors also acknowledged this: because cohort studies are observational (we are not able to experimentally manipulate every aspect of a person’s lifestyle or diet), then we cannot account for everything each person does in their daily lives that could affect their CVD risk. What we must do as readers of science is to think about whether there are unmeasured factors beyond this list that could affect people’s eating habits, and we can consider whether those variables might also be affecting CVD risk.
Although there remain some major barriers to making sure everyone benefits equally from a heart-healthy diet regardless of socioeconomic status, PolicyLink offers a few major policy steps in the right direction.
- Healthy Food Financing Initiative (HFFI) – This federal program partners with state and metro areas to support local strategies to bring supermarkets, co-ops, and farmers’ markets to improve access to nutritious foods to struggling communities.
- New Markets Tax Credit – This tax incentive has provided more than $400 million towards the development of healthy food retail in neighborhoods lacking a full-scale grocery store.
- Urban Gardens – According to a report by NPR, neighborhood gardening initiatives in D.C. and elsewhere have helped to educate people about food choices, and provide a source of affordable produce for neighbors.
Peer-reviewed by Mike Essman.