Eating a heart-healthy diet with olive oil can lower the risk of depression, says researcher Almudena Sanchez-Villegas, PhD, associate professor of preventive medicine at the University of Las Palmas de Gran Canaria in Las Palmas, Spain. The study included more than 12,000 people.
"The participants with an olive oil consumption higher than 20 grams a day (about 0.7 ounces) had a 30% lower risk of depression than those without consumption or with a very low consumption of olive oil," Sanchez-Villegas tells WebMD.
Those who took in the most trans fats, however, had up to a 48% increased risk of depression.
The unhealthy fats, says Sanchez-Villegas, are believed to lead to biological changes in the body linked with both heart disease and depression.
The researchers evaluated 12,059 men and women, with an average age of 37. All were free of depression at the start of the study.
The men and women completed a food frequency questionnaire, describing their intakes of various types of fat. After a median follow-up of 6.1 years (half were followed longer, half less) 657 new cases of depression had been diagnosed.
The researchers then looked at the type and amount of fat intake to see if it played a role. It did.
Those who ate a high amount of trans fat -- the fat type found in fast food, industrially produced pastries, and certain whole milk products -- had an increased depression risk, while those who ate the most olive oil had a lower risk than those with a low consumption of olive oil or no olive oil.
The trans-fat intake in the participants was fairly low, Sanchez-Villegas says. Those in the highest intake group took in about 1.5 grams daily, and it was in that group the researchers found the 48% increased risk of depression.
In the study, both good fats and bad showed what scientists call a ''dose-response'' relationship. "More consumption, more protection [for olive oil] and more intake, more risk [for trans fatty acids],'' Sanchez-Villegas says.
The biological changes that occur with high consumption of ''bad'' fats may explain both the heart disease and depression link, the researchers say.
The ill effects of bad fats on heart disease are believed to be due to increases in LDL “bad” cholesterol and reductions in HDL “good” cholesterol. There are also inflammatory changes, and these changes have also been linked with depression, the researchers say.
Inflammation may interfere with the brain's neurotransmitters, such as serotonin, Sanchez-Villegas says, and a lack of serotonin adversely affects mood.