The varied literature on the effects of omega-3 supplementation on depression can throw up conflicting results depending on the structure and size of the individual studies. Some researchers will look at the components of omega-3s together, some separately; some for two weeks and some for two months. In order to arrive at a coherent answer to the questions of the role of omega-3 fats on depression a group of Italian researchers conducted a meta-analysis. They pooled the studies conducted on patients with a diagnosis of major depressive disorder (MDD) and those who exhibited depressive symptoms but who did not have a clinical diagnosis. The average length of treatment with fish oils was 16 weeks. The analysis revealed a significantly positive effect of fish oils (particularly EPA) in alleviating symptoms in both patients with MDD and those without a diagnosis showing that these essential fats are an effective treatment for primary depression.

Grosso, G., Pajak, A., Marventano, S., Castellano, S., Galvano, F., Bucolo, C., Drago, F. & Caraci, F. (2014). Role of omega-3 fatty acids in the treatment of depressive disorders: a comprehensive meta-analysis of randomized clinical trials. PLoS One, 9 (5), e96905. ECollection.