The Mediterranean diet has long been the standard for heart healthy eating. It is a diet that emphasizes olive oil, fresh vegetables, nuts, whole grains over refined grains, fish and plant-based protein over red meat, herbs and spices to flavor food over salt, and fresh fruit for dessert instead of refined sweets. The US News and World Report even named the Mediterranean diet its number one diet for 2018. In addition to diet, the Mediterranean lifestyle incorporates moderate alcohol consumption, exercise and socialization with meals. There has been a lot of data to support the claim that this diet and lifestyle is good for heart patients. However recent revelations may have knocked the Mediterranean diet off its pedestal.
The most important and influential trial of the Mediterranean diet, the PREDIMED study, was published in 2013. The trial looked at 7,400 people who were at high risk for heart disease. They were randomized to either the Mediterranean diet or a reduced fat diet. After five years the trial was stopped early and in dramatic fashion. The Mediterranean diet was declared the winner because it lowered the risk for heart attack, stroke and cardiac death by a substantial 30 percent compared to the reduced fat diet. Reductions of this magnitude are rarely seen with medications much less with dietary therapy. Since this trial was published, cardiologists have prescribed the Mediterranean diet to their patients. PREDIMED was felt to be an excellent study providing rock solid evidence in a field (nutritional science) that is filled with flawed studies. However in a shocking and rare move in June 2018, the New England Journal of Medicine printed a retraction of the PREDIMED trial, questioning the outcomes. It turns out that about 1,500 patients (about 20%) were not properly assigned to the various diet groups. The researchers recalculated the data, without the 1,500 people, and found that the results were much the same, but the evidence was now much weaker.
Does the PREDIMED retraction nullify the Mediterranean diet? Does this mean that the diet is not beneficial for heart disease? Likely not. The Mediterranean diet remains the standard for heart healthy eating. Each of the components of the Mediterranean diet has been shown to be beneficial and make common sense for the heart patient. In separate and independent studies, fish, fresh fruit, vegetables, nuts, olive oil and plant based protein have all been shown to lower the risk for heart disease. In addition, the Mediterranean diet is nutritious and sustainable (people can follow it rather easily for years).
Another component of the Mediterranean diet, a glass of wine per day, has also recently come into question. A recent study looking at 600,000 current alcohol drinkers showed that imbibing seven or more glasses of wine per week was associated with an increased risk of death from all causes. The more alcohol consumed per week, the higher the risk of death. They estimated an upper safe limit of alcohol was five standard glasses of wine per week for both men and women. Drinking above that limit was associated with shorter life expectancy.
These new data and retractions point out that nutritional studies are notoriously difficult to perform. In general, there are several different problems with these studies. It is hard for people to eat the proper foods consistently without straying (ask anyone who has been on a diet). There is a huge influence of culture and society on what a person eats and the amount of alcohol consumed. There is a complex interplay between diet, alcohol and other behaviors (for example exercise and smoking). In addition, heart disease takes a long time to develop, so diet studies must be carried on for years to see a possible effect. Lastly, nutritional studies are often funded by industry and thus subject to bias. For example, a study sponsored by the National Institutes of Health looking at alcohol and heart disease was halted in June 2018 when it was discovered that it was partially funded by the alcoholic beverage industry.
Why is this important? It underscores the fact that even professional researchers, who are trying to conduct a scientifically sound study, have a hard time. Keep this in mind while reading the next sensational newspaper story touting the effects of the latest diet or watching television and hearing about the benefits of alcohol. Please evaluate these types of stories with some healthy skepticism.