A large (15,000 participants) Spanish study has shown that diets high in nutrients are linked to a reduced risk of depression. This study has generated a lot of interest not only because of the large cohort size, which makes the results more generalisable, but because it is thought to be the first to follow healthy individuals and track, over 10 years, those who went on to develop illness and disease.
The researchers looked at three diets:
Mediterranean Diet – characterised by the consumption of vegetables, legumes, fruits and nuts, cereals, fish and seafood; low intake of meat and dairy products, and moderate alcohol intake.
Vegetarian Dietary Pattern – a kind of ‘flexitarian’ diet that promotes eating plant foods (including potatoes) most of the time but allowing for a little meat
Healthy Eating Index- promotes eating larger amounts of vegetables, fruits, whole-grain bread, nuts, beans and pulses, omega 3s and unsaturated fats, and smaller amounts of sugar-sweetened beverages and fruit juice, red/processed meat, trans fats, and alcohol.
As part of the study the researchers also looked at activity levels, BMI, health history and vitamin supplementation, and the analysis was controlled for a number of variables including age, sex and smoking status.
For the statistical analysis the levels of adherence were split in to five groups (quintiles). So on a scale of 1-5, those in group 1 ate the least healthy diets while those in group 5 were paragons of healthy eating. The results showed that those in groups 2-5 had a 25-30% reduced risk of developing depression than those in group 1. Interestingly, there was a plateau in this effect once the respondents had moderately good diets. The researchers believed this to be due to a threshold effect; once you are consuming adequate amounts of a nutrient there is no additional benefit of consuming larger quantities of it.
The researches did not highlight any individual food or nutrient as being particularly important or protective. In fact they pointed out in their discussion the inconclusive results from other studies that looked at the relationship between individual nutrients (vitamins, minerals or fats) and depression. However, this and other studies have demonstrated the strong relationship between the quality of the overall diet and risk of depression. It is likely that it is the interaction of different compounds from various foods that offers most protection not just to depression but to overall health.
Sánchez-Villegas, A., Henríquez-Sánchez, P., Ruiz-Canela, M., Lahortiga, F., Molero, P., Toledo, E., & Martínez-González, M. (2015). A longitudinal analysis of diet quality scores and the risk of incident depression in the SUN Project. BMC Medicine, 13, 197-197.