This study shows that the consumption of hydrogenated oils (trans-fats) may be linked to depression. Hydrogenated oils and the trans-fats they create harden the arteries and increase the risk of heart disease and cancer. They also create inflammation, which may interfere with the brain's neurotransmitters, such as serotonin, which regulates mood. A lack of seratonin adversly affects mood.

The average consumer will consume a large amount of trans-fats in everyday foods if he/she isn't in the  habit of reading the list of ingredients in pre-made foods. Cookies, doughnuts, breads,margarines,shortetnings, potato chips, fried chicken, and French fries, are often made with highly manipulated, un-natural fats. 

Read the whole article at: http://www.webmd.com/food-recipes/news/20110126/eating-trans-fats-linked-to-depression

If consumers were to increase the use of extra virgin olive oil as a main source of fat,it may mean that their entire approach to food would be healthier.They would choose natural, single ingredients, cook more, take more time to eat, and thus, experience the pleasures and benefits of a healthy lifestyle which promotes healthy seratonin levels and good moods.