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 study is published online in PLoS ONE.
Diet 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.
The new research adds to a growing body of evidence about the importance of the type of fat eaten, says Jian Zhang, MD, DrPH, a researcher at Georgia Southern University in Statesboro, who has also studied the link between dietary fat and depression and published a study.
Increasingly, Zhang says, studies are ''suggesting physical health and mental well-being are sharing nutritional factors related to subtypes of fatty acids."
Studies have found some conflicting results. In Zhang's research, the epidemiologist found gender differences regarding fat intake and mood. Zhang found that an increased intake of oleic fatty acids, a monounsaturated fatty acid, was linked with a reduced risk of depressed mood among women, while an increase in linoleic fatty acids, an unsaturated fatty acid, was linked with an increased risk of depressed mood among men.
Despite the conflicting results, Zhang says, ''almost all evidence, anecdotal or scientific, consistently pointed out olive oil is good."
Sanchez-Villegas says the study looked at university graduates in a Mediterranean setting, so the finding of high olive oil intake is not surprising.
Their consumption of trans fats was fairly low overall. The intake in the highest of the five groups was 1.5 grams a day, and that amount is low compared to other populations, including the U.S., Sanchez-Villegas says.
For that reason, the suggestion to watch your intake of trans fat might be especially important, Sanchez-Villegas says, in the U.S. and other locations where the population tends to eat higher amounts.