A new study from researchers at Rush University Medical Center has found that people following a healthy diet designed to reduce their risk of hypertension also display associated lower rates of depression. The new study adds to a growing body of evidence suggesting strong links between diet and mental health.

The Rush University study was primarily focused on what is called the DASH (Dietary Approaches to Stop Hypertension) diet. Developed to lower blood pressure without medication, the diet centers on limiting sodium intake and eating lots of fresh fruits and vegetables, as well as whole grains and low-fat dairy. It was recently ranked as one of the healthiest diets overall by a panel of experts examining 40 of the most common diets.

The study followed 964 subjects for over six years, evaluating them annually for symptoms of depression as well as looking at how closely they followed various diets, including DASH, the Mediterranean diet and a conventional Western diet. All the subjects were divided into three groups depending on how closely they followed their selected diet, and it was found that those who most closely followed the DASH diet were the least likely to develop depression compared to other groups.

Author of the study, Laurel Cherian, does note that this is only an associational observation and does not at this stage confirm that the diet actively reduces depression. It's clear that any correlation between diet and depression raises a fundamental causal question. Does a bad diet actively make a person depressed or is a bad diet simply a symptom of depression?

A recent trial from researchers at Deakin University set out to investigate exactly that question by recruiting 67 adults diagnosed with major depressive disorder and splitting them into two groups. One group followed a healthy Mediterranean-style diet high in fresh fruit, vegetables, fish, lean meats and nuts. The other group underwent a structured social support program proven to be helpful for those with depression.

After three months the results came in. A third of the subjects undergoing the dietary intervention were identified as having entered remission for their depression compared to only 8 percent in the social support group.

"These results were not explained by changes in physical activity or body weight, but were closely related to the extent of dietary change," says one of the authors on the study, Felice Jacka. "Those who adhered more closely to the dietary program experienced the greatest benefit to their depression symptoms."

Despite these individual studies finding connections between depression and diet, a large meta-analysis of 24 studies published last year found only mild correlations confirming a healthy diet may lower the risk of depressive symptoms. But, significantly, the meta-analysis did not find any association between a low-quality diet and higher rates of depression.

There is certainly a growing body of evidence suggesting our gut bacteria plays a more prominent role in our neurochemistry than ever previously thought. Gut bacteria has recently been linked to PTSD and Alzheimer's disease, while a small study has shown probiotics can reduce symptoms of depression.

Whether an unhealthy diet actively causes depression is still yet to be determined, but the overall health benefits of a better diet are not in doubt and there is a lot to still be uncovered about the connections between our diet, gut and mental health.