By Elizabeth Nolan Brown, for Blisstree.com

Omnivores, take note: Embracing a vegetarian diet could make you happier and less stressed, according to new research published in Nutrition Journal.

The reason comes down to fatty acids: Diets that include meat and fish are higher in arachidonic acid (AA), an animal source of omega-6 fatty acids. Much of the meat Americans eat today is quite high in AA: The average omega-6 to omega-3 fatty acid profile of modern grain-fed meat is 5 times higher than grass-fed meat, like our ancestors ate. And previous research has shown high levels of AA can cause mood-disturbing brain changes.

High-fish diets also mean higher levels of long-chain, or omega-3 fatty acids, like eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). Both EPA and DHA combat the negative effects of AA. High dietary levels of omega-3 fatty acids are linked to better brain health, better mood and a host of other health benefits. Most health experts recommend an omega-6/omega-3 ratio of about 4:1.

In theory, then, frequent fish eaters should have be protected against the damaging effects of AA because of their higher intake of omega-3 acids. But an earlier study found omnivores reported significantly worse moods than vegetarians, despite higher intakes of EPA and DHA.

In this follow-up study, 39 meat-eating participants were assigned to one of three diets. A control group ate meat, fish or poultry daily; a second group ate fish 3-4 times weekly but no meat; and a third group ate strictly vegetarian. After two weeks, mood scores were unchanged for the fish- and meat-eating groups, but vegetarians reported significantly better moods and less stress.

“Restricting meat, fish, and poultry improved … short-term mood state in modern omnivores,” the researchers concluded.

After two weeks on a vegetarian diet, participants had “negligible amounts” of EPA, DHA and AA in their bodies. Fatty acid levels in the control group were unchanged. Participants in the fish eating group showed 95 to 100% higher levels of EPA and DHA fatty acids—but their omega-6 to omega-3 ratios were still heavily skewed toward omega-6′s.