Wouldn't it be nice if you could improve your mental health just by eating more fish?
Well, yes, it would... except for people who hate fish, who would be doomed to misery. But is it true? A new paper from Finnish researchers Suominen-Taipale et al looks at this issue: Fish Consumption and Omega-3 Polyunsaturated Fatty Acids in Relation to Depressive Episodes: A Cross-Sectional Analysis. The results are complex, but essentially, negative.
The authors looked at a large sample (total n=6,500) of Finnish people from the general population, and asked them questions about their diet, and their mood. They found a correlation between the amount of fish a person reported eating, and their likelihood of self-reporting depressive symptoms. However, this should be taken with a pinch of salt, a slice of lemon and a light cheese sauc...sorry. This should be taken with a pinch of salt, because it was only true in men, and it was only statistically significant using some measures of fish eating, not others.
Also, there was zero correlation between blood levels of omega-3 fatty acids, and depression, even in men. Omega 3's are considered to be the good stuff in (oily) fish, and are currently being promoted as good for your brain, your mood, your IQ, etc. by health food fans.
To be fair, it's completely plausible that eating lots of them is good for you, because they are known to be involved in nerve cell function. And there are many papers finding them to be a good thing. But this study is not one of them. (The same authors also have another paper out finding no correlation between fish eating or omega 3 and "psychological distress", but it's largely overlapping data.)
The authors conclude that fish may be beneficial to mental health in men, albeit not through omega-3 fatty acids. They suggest that fish may instead provide some kind of high-quality protein or minerals. However, the other explanation is that fish is just correlated with depression because eating fish is a marker for some other lifestyle factors:
The observed association between high fish consumption and reduced risk for depressive episodes in the men may indicate complex associations between depression and lifestyle which we were not able to take into account. Diet and fish consumption may be a proxy for factors that have effect on mental well-being particularly in men. A plausible explanation is that fish consumption in men is a surrogate marker for some underlying but yet unidentified lifestyle factors that protect against depression.
I think it's fair to say that the jury is still out on the benefits of omega 3's. As a vegetarian I don't eat fish and I have a history of depression and take not one, but two, antidepressants, so maybe I'm living proof that a lack of fish is a bad thing. I don't think so, though, as I took omega 3 supplements for a few months and felt no different. I gave up because they were costing me £30 a box.
Suominen-Taipale, A., Partonen, T., Turunen, A., Männistö, S., Jula, A., & Verkasalo, P. (2010). Fish Consumption and Omega-3 Polyunsaturated Fatty Acids in Relation to Depressive Episodes: A Cross-Sectional Analysis PLoS ONE, 5 (5) DOI: 10.1371/journal.pone.0010530