A dose-response relationship was observed, meaning "the more fast food you consume, the greater the risk of depression," explained Almudena Sánchez-Villegas, lead author of the study, which was published in the journal Public Health Nutrition. However, "Even eating small quantities is linked to a significantly higher chance of developing depression."
The study found that those who eat the most fast food and commercial baked goods are more likely to be single, less active and have poor dietary habits, which include eating less fruit, nuts, fish, vegetables and olive oil. They also tend to smoke and work more than 45 hours per week.
The study sample consisted of 8,964 participants who had never been diagnosed with depression or taken antidepressants. They were assessed for an average of six months, and 493 were diagnosed with depression or started to take antidepressants.
This new data supports the results of a similar project in 2011, which were published in the PLoS One journal. That project recorded 657 new cases of depression out of the 12,059 people tracked over more than six months.
Sánchez-Villegas concludes that "although more studies are necessary, the intake of this type of food should be controlled because of its implications on both health (obesity, cardiovascular diseases) and mental well-being."
Little is known about the role that diet plays in developing depressive disorders, but previous studies suggest that certain nutrients could play a preventative role. These include B vitamins, omega-3 fatty acids and olive oil -- all of which are lacking in a diet high in fast food and commercial baked goods.
And no, ordering olives on your pizza is not the solution.
Follow Samantha Bonar @samanthabonar.