The idea that depression and all of its relatives are manifestations of glitches in the immune system and inflammatory pathways – not a neurochemical deficiency disorder – is a topic I explore at length throughout my book, A Mind of Your Own

This fact is not as new as you might think, but it’s probably not something your general doctor or even psychiatrist will talk about when you complain of symptoms and are hurried out of the office with a prescription for an antidepressant.

A multitude of studies now show an undeniable link between gut dysfunction and the brain, chiefly by revealing the relationship between the volume of inflammatory markers in the blood and risk for depression. Higher levels of inflammatory markers, which often indicate that the body’s immune system is on high alert, significantly increase the risk of developing depression. And these levels parallel the depth of the depression: higher levels equates with more severe depression. Which ultimately means that depression should join the ranks of other inflammatory disorders including heart disease, arthritis, multiple sclerosis, diabetes, cancer, and dementia. And it’s no surprise, at least to me, that depression is far more common in people with other inflammatory and autoimmune issues like irritable bowel syndrome, chronic fatigue syndrome, fibromyalgia, insulin resistance, and obesity. All of these conditions are characterized by higher levels of inflammation.

To really grasp the fact that depression is not a disorder primarily rooted in the brain, look no further than some of the most demonstrative studies. When scientists purposefully trigger inflammation in the bodies of healthy people who exhibit no signs of depression by injecting them with a substance, they quickly develop classic symptoms of depression. And when people with hepatitis C are treated with the pro-inflammatory drug interferon, as many as 45 percent of those individuals develop major depression.

Depression: It’s a Lifestyle-Body Mismatch

So when people ask me about why we’re suffering from what appears to be an epidemic of depression despite the number of people taking antidepressants, I don’t think about brain chemistry. I turn to the impact of our sedentary lifestyles, processed food diets, and unrelenting stress. I turn to the medical literature that says a typical Western diet – high in refined carbs, unnatural fats, and foods that create chaos in our blood sugar balance – contribute to higher levels of inflammation.

Contrary to what you might assume, one of the most influential risk factors for depression is unstable sugar. Most people view diabetes and depression as two distinct disorders, but new scientific findings are rewriting the textbooks. One game-changing study published in 2010 that followed more than 65,000 women over a decade showed that women with diabetes were nearly 30 percent more likely to develop depression. This heightened risk remained even after the researchers excluded other risk factors such as lack of physical exercise and weight.

Personalized lifestyle medicine that accounts for the role of the environment in triggering inflammation and the manipulation of the immune and endocrine systems is the most sensible way to approach those individuals who would otherwise be candidates for multiple medications. It turns out that it may not all be in your head – but rather in the interconnectedness among the gut, immune, and endocrine systems.

It’s time we rewrite the textbooks. And it’s time we treat depression for what it really is!