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All,

 

Dr. Greger had another fascinating video out today on the link between inflammation and depression, and why an anti-inflammatory diet might be effective for treating depression. 

 

Apparently, it has long been known that systemic inflammation and depression are pretty highly correlated. And apparently, based on several studies cited in the video, you can induce depression in people by increasing the inflammation level in their bodies.

 

Researchers have made an argument for why evolution might have set it up this way. Throughout our evolutionary history, systemic inflammation has been almost exclusively associated with infections of some sort, many of which are contagious. When we develop an infection, and our body responds with an inflammatory response, it would have been 'good' for our kin (and therefore our genes, which they share), if we felt crappy, and all we wanted to do is curl up in a corner and avoid contact with other people - in order not to infect them. So, the evolutionary theorists say, we developed a mechanism by which systemic inflammation triggers a depressed mood.

 

Fast forward to today. We've pretty much defeated pathogenic infections, but still feel like curling up and dying when we get an infection - not much we can do about that. But in addition, despite few pathogenic infections, the bodies of most people are still inflamed continuously these days, largely as a result of the crappy diet most people eat. So the same depressive response to inflammation that used to provide a survival advantage, now simply makes us depressed, as a result of the food we're eating.

 

Not surprisingly, Dr. Greger goes on to advocate an anti-inflammatory diet centered around whole plant foods. He says meats in general, and even fatty fish, are proinflammatory for a variety of reasons, including endotoxins. He says that may be why the early hopes for fish and fish oil as a treatment for depression haven't seemed to pan out in larger studies.

 

I thought the most interesting graphs in the whole video are shown below, taken from [1]. In this study, researchers injected into human subjects an endotoxin derived from E. Coli, and then measured both their blood markers of inflammation and their mood over the next few hours. As their bodies mounted an inflammatory response to the endotoxin (as indicated by the IL-6 and TNF-a markers of inflammation), subjects reported a depressed mood. As the inflammation subsided, so did the depressed mood. The correlation between the inflammation and the depressed mood was high, and wasn't observed in the subjects injected with a placebo. 

 

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I thought it was a really thought provoking video, and a reasonable explanation for the mystery of why depression might have evolved and persisted in our highly social species.

 

Maybe the fact that CR practitioners generally eat a highly anti-inflammatory diet, and have low levels of inflammation as measured by blood tests like C-reactive protein (CRP), may explain why, after the initial weight loss period when toxins may be released from the fat we're losing, triggering inflammation and therefore depressed mood, CR practitioners generally report being in very good moods - quite in contrast to the expectation most people have that CR would make you permanently irritable.

 

Finally, I don't want to oversimplify true clinical depression - which is an incredibly complex and debilitating condition. The kind of "depression" Dr. Greger is talking about in this video and that may be associated with chronic inflammation might be better characterized as "depressed mood", as opposed to true clinical depression. For more info on some of the complexities of clinical depression, including its genetic component, check out this short video on the science of depression.

 

 

--Dean

 

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[1] Brain Behav Immun. 2010 May;24(4):558-63. doi: 10.1016/j.bbi.2009.12.009. Epub

2010 Jan 4.

Inflammation and social experience: an inflammatory challenge induces feelings of
social disconnection in addition to depressed mood.

Eisenberger NI(1), Inagaki TK, Mashal NM, Irwin MR.

Free full text: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2856755/

Although research has established links between feelings of social isolation and
inflammation, the direction of these effects is unclear. Based on the role that
proinflammatory cytokines play in initiating "sickness behavior," which includes
symptoms such as social withdrawal, it is possible that inflammatory processes
heighten feelings of 'social disconnection.' Here, we examined whether exposure
to an inflammatory challenge increased self-reported feelings of social
disconnection. In addition, because both inflammatory processes and feelings of
social disconnection contribute to depressive symptoms, we also explored whether
increases in feelings of social disconnection played a role in the link between
inflammation and depressed mood. Participants were randomly assigned to either
receive endotoxin, an inflammatory challenge, or placebo. Proinflammatory
cytokines (IL-6, TNF-alpha) were collected at baseline and then hourly for 6h.
Participants completed self-reports of sickness symptoms ("fatigue"), social
disconnection ("I feel disconnected from others"), and depressed mood ("unhappy")
hourly. Results revealed that endotoxin led to significant increases (from
baseline) in IL-6 and TNF-alpha levels as well as feelings of social
disconnection and depressed mood. Moreover, controlling for increases in social
disconnection eliminated the relationship between exposure to inflammatory
challenge and depressed mood. This study demonstrates that inflammation can have
social psychological consequences, which may play a role in cytokine-related
depressive symptoms.

Copyright 2009 Elsevier Inc. All rights reserved.

PMCID: PMC2856755
PMID: 20043983

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