Trans fats can be transformative, and not in a good way. These unhealthy fats—which can lurk in margarines, fast foods, doughnuts, and other baked goods—raise the risk of heart disease by upping bad cholesterol and lowering good. Now, a new study suggests another possible trans-fat transgression: a raised risk of depression.
Researchers followed 12,059 graduates of Spanish universities for several years, using questionnaires to assess their diet, lifestyle, health, and whether they'd been diagnosed with depression. They then analyzed this data to see whether there was a connection between what fats people ate and their chance of depression.
The findings suggested a close link. The higher the amount of trans fats people ate, the greater their risk of depression
. And those who consumed the highest levels of trans fats were 48 percent more likely to be diagnosed with depression than those who consumed the least.
On a positive note, the researchers found an opposite relationship with unsaturated fats, such as those in olive oil. The more of these healthy fats people ate, the lower their risk of depression.
So did trans fats actually increase people's risk of depression (and did unsaturated fats lower it)? It's too soon to say. Many things can influence a person's chance of depression, and we don't yet know whether people's fat intake—and not something else—was what accounted for the differences in the study.
However, the researchers did take into account several factors that might have affected people's risk, including how much they exercised, their body mass index (BMI), whether they smoked, and how healthy their diet was in other respects (for example, whether they adhered to a Mediterranean-style diet). Still, they didn't look at other important factors, such as people’s economic status or where they lived. Dietary choices might simply reflect having less money, or living in a more deprived area. Both of these things could increase the chances of depression.
More studies will need to sort out these findings and also explore whether they apply to people in other countries, with different types of diets. In the United States, for example, trans fats account for a much higher percentage of people's total energy intake: around 2.5 percent, by some estimates, compared with only 0.4 percent for people in this study. If there is indeed a link between trans fats and depression, this could mean that Americans are at an even higher risk.
What you need to know. We already know that avoiding trans fats is good for your heart. This study suggests it might help your mental health too.
—Sophie Ramsey, patient editor, BMJ Group
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For more information, take a look at our guide to fats in food.