What You Eat May Promote Depression

Previous work has suggested that consumption of trans-unsaturated fatty acids (trans-fats) is linked to an increase in the risk of depression.  And trans-fats have been removed from most foods in the USA.  But does this mean that mono- and poly-unsaturated fatty acids could have a protective effect against the risk of developing depression?  Spanish investigators have conducted a definitive study and reported it in PLoS ONE, the online medical journal. 

This was a prospective study of over 12,000 Spanish university graduates (average age 37½) who were initially free of depression. At baseline they were given a 136-item food frequency questionnaire which was used to determine the intake of fatty acids and fats used in cooking. The former included saturated, polyunsaturated, trans-unsaturated, and monounsaturated fatty acids; the culinary fats included olive oil, seed oils, butter, and margarine. The students were followed for an average of 6 years, during which time 657 new cases of depression were diagnosed and confirmed. The risks of developing depression – hazard ratios – were calculated for the intake of the different fats by constructing five classes, or quintiles, for each fat.

The hazards ratio for depression across successive quintiles of trans-fat intake were 1.0 (the lowest intake quintile), 1.08, 1.17, 1.28, and 1.42; this shows a clear "dose-dependent" relationship between trans-fat intake and the risk of developing depression. On the other hand, similar but inverse relationships were obtained for the intake of monounsaturated and polyunsaturated fatty acids, so that a protective relationship was shown between increasing intake of these two types of fatty acids and a reduced risk of depression; the same inverse relationship was found for olive oil intake.

These findings mimic those that would be expected from similar studies of the effects of fats in the diet and cardiovascular risk, and confirm the detrimental role of trans-unsaturated fatty acids as well as the beneficial effects of olive oil, mono- and polyunsaturated fatty acids. There are therefore at least two good reasons for eating a healthy diet, as far as the fat content is concerned. One can summarize the practical steps as follows: consume olive oil rather than butter or margarine, use low-fat dairy rather than high-fat dairy products, and eat fish rather than meat or meat products; avoid fast and processed foods and commercial bakery products, and increase consumption of fruits, vegetables, and nuts.