Feel like a nut? Walnuts contain healthy fats that may boost your mood.

RODALE NEWS, EMMAUS, PA—How’s this for a downer statistic: More than a quarter of all Americans suffer from diagnosable mental health issues. Many are treated with prescription antidepressants to the tune of about $12 billion, which is what Americans spend on these mood-boosting medications every year. But a new study finds that if we spent all that money on vegetarian diets rather than pills, we might be less depressed.

THE DETAILS: For the report, which appears in the June 2010 issue of Nutrition Journal, researchers studied 138 Seventh Day Adventists living in the Southwest (60 vegetarians and 78 meat-eaters). This religious group is often studied because its members are relatively consistent in their lifestyle characteristics, which allows researchers to account for external influences more easily. The volunteers were asked to complete questionnaires about their diet; their levels of depression, anxiety, and stress; and their general mood states.

The researchers found the vegetarians reported diets significantly lower in EPA and DHA, the omega-3 fatty acids that we get from eating fish, and which many studies have found are a key factor in improving both physical and mental health. So they expected to find the vegetarians would have higher incidences of issues like depression, anxiety, and mood problems. Instead, they found the opposite result. Vegetarians scored lower on depression tests and had better mood profiles than their fish- and meat-eating peers. "While dietary intake of EPA and DHA has an important role in brain function, we found no evidence that the absence of direct intake of these fatty acids in vegetarians adversely affects mood state," the study reports. "These results challenge what is known about the link between dietary fats and brain function and suggest an unrecognized benefit of vegetarian diets."

WHAT IT MEANS: It was previously believed that plant-source omega-3s, found in nuts, flax, and oils, are less effective in boosting brain and physical health than EPA and DHA, since it’s harder for our bodies to convert these plant sources into usable amino acids. But this new study seems to turn that logic on its head. One reason could be the strict adherence that Seventh Day Adventists have to not just a vegetarian diet, but a healthy one at that. "The Seventh Day Adventists have been eating this vegetarian diet for a long time, and they don’t go about it the way many other vegetarians do," says the study’s lead researcher, Bonnie Beezhold, PhD, MPH. They don’t just eliminate meat and replace it with unhealthy, meat-free processed foods, she adds. They incorporate lots of fruits and vegetables and round their meals out with a variety of other healthy foods like healthy oils and nuts that are rich in the plant-based omega-3 alpha-linolenic acid (ALA). The diets are also low in arachidonic acid (AA), she says, which is found in factory-farmed meat and been associated with a host of problems, including mental health issues and inflammation in the body.