Trans-fats may be every bit as bad for the head as they are for the heart. A Spanish study looking at new cases of depression found that people who ate the most trans-fats were likeliest to develop depression over a six-year period. Those who ate the most trans-fats were 48% more likely to be diagnosed with depression than those who ate the least trans-fats.
Increased trans-fat consumption was associated with increased risk of depression. The results also showed a smaller but statistically significant protective effect from depression as people ate more polyunsaturated fats.
Only tiny amounts of trans-fats occur naturally in food. The rest are man-made additives. They're often added to baked goods such as cakes, cookies and pastries, though they can turn up in almost any processed food. Margarine and shortening usually contain trans-fats. The term "partially hydrogenated vegetable oil" on a food label is a dead giveaway that a food has trans-fat in it. It's been known for years that trans-fats are bad for the heart and circulation, but little research has been done on their effects on the mind.
The SUN project is a multi-faceted ongoing health study begun in 1999. Participants are all university graduates from Spain. This portion of the study focused on the relationship between types of fat in the diet and occurrence of depression.
From their food questionnaires, individuals' levels of consumption of four types of fats (trans, saturated, monounsaturated and polyunsaturated) were estimated. The fat consumption pattern of people who developed depression was then compared to the fat consumption of the rest of the participants.
Increased trans-fat consumption was associated with increased risk of depression. The results also showed a smaller but statistically significant protective effect from depression as people ate more polyunsaturated fats. An even weaker but still statistically significant protective effect was found from increased monounsaturated fat consumption and specifically, olive oil consumption.
In short, the results suggest the possibility that high amounts of trans-fat in the diet increases the risk of depression while higher consumption of monounsaturated and polyunsaturated fats may protect against it.
Foods high in monounsaturated fat include olive and canola oil. Most vegetable oils and fish are high in polyunsaturated fat. Meat and dairy products, as well as palm and coconut oil, are the main dietary sources of saturated fat.
If trans-fats do cause depression, the effect would most likely be stronger in the U.S. than in Spain. Spain is a Mediterranean country and Spaniards are more likely to eat a Mediterranean diet than a Western diet. The amount of trans-fats consumed by study participants in this study was low, about 0.4% of total energy consumption. Trans-fat consumption in the U.S. has been estimated to be as much as six times higher.
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An article on the study was published by the open-access journal PLoS ONE on January 26, 2011 and is freely available.