A research article published in The New England Journal of Medicine on February 25, 2013 found that a traditional Mediterranean diet reduced risk of major cardiovascular events compared to a low-fat diet. The study suggested that a Mediterranean diet — rich in olive oil, nuts, beans, fish, fruits and vegetables — is healthier than a typical western diet. The study also demonstrated the challenges of conducting clinical research trials on diet.
Researchers recruited nearly 7,500 participants ages 55 to 80 and at high risk for cardiovascular disease. Three diets were included in the study: a Mediterranean diet with high olive oil consumption, a Mediterranean diet with high nut consumption, and a low-fat diet. Unfortunately, the low-fat diet was not truly low in fat. On average, low-fat dieters reduced their fat intake from 39% to 37% of calories. By USDA standards, a low-fat diet contains less than 30% of calories from fat. Thus, this study is probably a better comparison of a typical western diet versus Mediterranean diets.
Researchers found a significant reduction in major cardiovascular events, particularly stroke, in individuals following either of the Mediterranean diets. After tracking participants for an average of 4.8 years, 288 suffered major cardiovascular events. Of those 288 individuals, 96 events (risk ratio= .72) occurred in the high olive oil Mediterranean group, 83 events (risk ratio= .70) occurred in the high nut Mediterranean group, and 109 events occurred in the control group.
The results indicated the Mediterranean diet is healthier, in terms of cardiovascular events, than the failed attempt at a low-fat diet. The results also seem to indicate that a Mediterranean diet is easier to follow than a low-fat diet, but there was a confounding factor in that the Mediterranean dieters were provided with more diet training sessions than the low-fat dieters.
With obesity and diet-related diseases increasing at an alarming rate, the USDA continues to promote the low-fat diet, as it has for decades. In a New York Times article about the study, Dr. Steven E. Nissen, chairman of the department of cardiovascular medicine at the Cleveland Clinic Foundation, pointed out that low-fat diets have not been shown in any rigorous way to be helpful, and they are also very hard for patients to maintain.
Despite advances in other scientific fields, nutrition has lagged behind, in part, because clinical nutritional studies are difficult to conduct. For example, these researchers wanted to study a low-fat diet but the participants could not adhere to the diet. Genetics confounds every human diet study because we cannot control for genetic differences between humans that might affect disease risk. Additionally, diets may have different effects on individuals with different genetic backgrounds. Varying environmental factors might also affect disease risk.
How can we learn about the effects of various diets when there are so many factors present in human clinical trials? This is the question I am attempting to answer through my dissertation research at North Carolina State.
In my study, I am using mice to compare the health effects of different diets. Mice are model systems for diet studies because their digestive tracks are similar to humans and they share many genes with humans. Mice in studies cannot cheat on their diets, and both genetic and environmental factors can be controlled in mouse studies.
My study involves feeding six different types of diets (Control, Western, Mediterranean, Japanese, Hunter-Gatherer, Ketogenic) to mice of different genetic backgrounds, and collecting data on a wide variety of physiological parameters (metabolic and inflammatory markers, organ health, gene expression, physical activity, endurance, sleep, etc.). We can then compare mouse data with human diet studies to gain a much clearer picture of how diet affects health. The study is currently underway with help from collaborators at the University of North Carolina. Stay tuned for updates!