Rodale has the scoop on this study
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."