Eating poor food can put you in a low mood, new research has suggested.
Scientists have found a link between consuming harmful trans-fats and an increased risk of depression.
But olive oil and healthier polyunsaturated fats appear to have the opposite effect, helping to keep people cheerful.
The research may provide a clue to why southern Europeans tend to be less depressed than northerners, say the researchers.
Mediterranean diets are rich in healthy ingredients such as fish, fresh fruits and vegetables, as well as olive oil.
People in the UK and other northern European countries, on the other hand, are more likely to consume foods laden with saturated and trans-fats.
Trans-fats are modified vegetable fats used to improve shelf-life and often found in fast foods, pastries, cakes and biscuits.
They are strongly linked to raised levels of “bad” cholesterol and heart disease.
The new research was carried out by Spanish scientists who studied more than 12,000 university graduate volunteers over six years, recording details of their diets, lifestyles and illnesses.
The findings are published in the online journal Public Library of Science ONE.