Chris Kresser: Yeah, I think what you’re referring to, Justine, is the gut-brain axis and connection and then the inflammatory cytokine model of depression. You summarized it pretty well. Inflammatory cytokines produced in the gut travel through the blood, and they cross the blood-brain barrier, and then they suppress activity in the frontal cortex. A lot of our higher brain functions, of course, are governed by the frontal cortex, and so when you have suppressed activity of the frontal cortex, that leads to symptoms that are analogous with depression and can also lead to decreased cognitive function and executive function.
The inflammatory cytokine model of depression is definitely one that has really assumed a high level of importance in the overall understanding of depressive pathology, and a lot of researchers and clinicians feels like it probably accounts for a substantial percentage of cases of depression that we see. I don’t think that I would go as far as to say that all depression is caused by this inflammatory cytokine model. I think depression is a multifactorial condition, and certainly there’s situational depression, there’s seasonal affective disorder, there’s depression that’s caused by pretty terrible life circumstances, trauma, emotional and psychological issues, but I think one of the problems here is that we’re hampered by our language. In our language, unfortunately, we make a separation between physiology and psychology, but in reality, there is no separation. You can’t say something is exclusively psychological or exclusively emotional and not at the same time physiological, just as you can’t say something is physiological and not simultaneously emotional and psychological. Any thought or feeling that we have or experience we’re experiencing physiologically, and physiological effect that occurs, like inflammation, is going to produce thoughts or emotions and change our psychology and our emotional state. In Chinese medicine, there’s not really even a clear separation between mind and body, and they looked instead at patterns based on organ systems, and I think they were pretty far ahead in this regard. We have a system of medicine that’s based on Cartesian dualism, and it unfortunately really sent us in the wrong direction and has led to this kind of compartmentalized approach where we see the mind as separate from the body. I think part of what our task is as functional medicine providers is to move people into a more holistic view, where we aren’t seeing a separation between mental, emotional, and physiological, and we’re addressing all of these things to the best of our ability simultaneously.