June 25, 2003 -- In the largest study ever done on the Mediterranean diet and one of the few to test it in adults of all ages -- in Greece, no less -- researchers found that the real bang of this ballyhooed magic bullet appears not to be olive oil but a combination of all food in the diet.
Scores of studies suggest that the high-fat Mediterranean diet translates to a slimmer risk of heart disease and cancer. And olive oil has sometimes gotten the lion's share of credit -- possibly undeservedly, according to the new findings.
The olive oil-drenched diet is believed to be why residents of the 16 countries that border the Mediterranean Sea typically live longer than Americans and have lower rates of these diseases -- despite consuming a high-fat diet. The theory: Most of the fat comes from monounsaturated fat, the type in olive oil that -- unlike saturated fats -- is heart-healthy and may have cancer-prevention effects.
Not surprisingly, the researchers found that Greeks who follow the Mediterranean diet more closely have significantly lower death and disease rates than those who don't. But they also report in this week's issue of TheNew England Journal of Medicine that olive oil itself produced no significant reduction in overall death rates.
"Olive oil plays a central role, but it is not alone," says Dimitrios Trichopoulos, MD, PhD, of Harvard School of Public Health.
"It's among the divine mix of several factors that, when used in combination, help provide strong evidence of something that is very important -- eating the proper diet can significantly reduce your risk of early death."
He and researchers from Greece studied some 22,000 adults, aged 20 to 86, from all regions of that country; most previous studies tracked only older people who were more likely to die during the study. The participants answered detailed questionnaires about their eating habits throughout the four-year study. Then they were rated on how closely they followed the key principles of the Mediterranean diet.
Sticking to the Mediterranean diet cut the risk of death from both heart disease and cancer. For every two points higher on this 0-to-9 scale -- with top numbers going to those most closely following the Mediterranean diet -- the death rate dropped by 25%.
So what does that mean exactly? Substantially increasing the intake of monounsaturated fats relative to saturated fats and reducing in intake of meat would do the trick.
Olive Oil, Fish, Veggies ... What Is It?
When the researchers looked at the individual components of the Mediterranean diet, they found no significant decrease in death with any one type of food.
In addition to having olive oil with most meals, the typical Mediterranean diet is very high in vegetables, fruits, legumes, nuts, and cereals; moderate in fish intake; and has lower amounts of meat and dairy than the typical American diet. Drinking alcohol is also a frequently practiced dining ritual.
"God knows what sorts of interactions take place within the foods, and we need further research to pinpoint them exactly," Trichopoulos tells WebMD.
"But typically, people in Greece eat twice as many vegetables as Americans -- nearly a pound a day. And you really can't eat a pound of vegetables a day unless you have olive oil to make them appetizing. My advice is to try to double the amount of vegetables and fruits you currently have, and eat more fish, legumes, and non-refined cereals."
While olive oil itself showed little benefit, the researchers note a significant reduction in death rates from a higher overall ratio of monounsaturated fats to saturated fats. Olive oil is among the best sources of monounsaturated fats -- and happens to be the main cooking oil in most Mediterranean countries -- but other oils frequently consumed by Greeks and others surrounding the Mediterranean Sea also contain these healthy fats.
Calories Versus Healthy Oils
Trichopoulos' finding may also help explain why Asians, who typically use these other cooking oils, also have lower disease and death rates. Although they rarely use olive oil, they traditionally follow other principles of the Mediterranean diet -- lots of produce, legumes, nuts, and minimally processed grains, with little saturated fat.
"The message remains the same, and is consistent with other findings: A diet lower in saturated fats and higher in monounsaturated fats, and potentially, polyunsaturates, will result in better health outcomes," says Alice H. Lichtenstein, DSc, of Tufts University and a spokeswoman for the American Heart Association.
"If the main message that Americans get is to just increase their olive or canola oil consumption, that's unfortunate because they will increase their caloric intake and they are already getting too many calories. What they need to do is eat more fruits, vegetables, and legumes and fewer foods rich in saturated fats."