A diet of fast food, cakes and processed meat may significantly increase risk of depression, a study has found.
Researchers from Manchester Metropolitan University in the UK found that eating foods which are known to promote inflammation—such as those high in cholesterol, saturated fats and carbohydrates -- puts people at 40 per cent higher risk of depression.
The team analysed data from 11 existing studies that focused on the link between depression and pro-inflammatory diets—encompassing more than 100,000 participants, between 16 to 72 years old, of varied gender and ethnicity, spanning the USA, Australia, Europe and the Middle East.
All the studies recorded the presence of depression or depressive symptoms in the participants—through self-observation, medical diagnoses and antidepressant use --alongside a detailed questionnaire about the contents of their diet.
Each participant was assigned a score of how inflammatory his or her diet is, according to the dietary inflammatory index.
Some of the studies were cross-sectional, using data that was immediately available, and other studies tracked participants for up to 13 years.
Across all studies, participants who had a more pro-inflammatory diet were, on average, 1.4 times more likely to have depression or depressive symptoms.
The results, published in the journal Clinical Nutrition, were consistent regardless of age or gender—and were the same over both short and long follow-up periods.
"These results have tremendous clinical potential for the treatment of depression, and if it holds true, other diseases such as Alzheimer's which also have an underlying inflammatory component," said Steven Bradburn from Manchester Metropolitan University.
"Simply changing what we eat may be a cheaper alternative to pharmacological interventions, which often come with side-effects," said Bradburn.
An anti-inflammatory diet -- containing more fibre, vitamins (especially A, C, D) and unsaturated fats -- has the opposite effect, and could be implemented as a treatment for depression, researchers said.
Therefore, a Mediterranean diet of olive oil, tomatoes, green vegetables and fatty fish could help lower depressive symptoms.
Inflammation is the body's natural defence system against infections, injuries and toxins. In order to protect itself from harm, the body releases proteins, antibodies and increased blood-flow to affected areas, causing redness and swelling.
However, chronic inflammation puts the body in a constant state of alert and has previously been linked to diseases such as cancer, asthma and heart disease. Such persistent inflammation, particularly in the brain, is believed to contribute to neuronal death.