Fewer gut microbes = more stress hormones?
Researchers at Cal Tech have identified a specific circuit of neurons directly influenced by the gut microbiome and responsible for antisocial behaviors in mice that lack a gut microbiome. Transplants of fecal matter from mice with healthy gut microbiomes were sufficient to change the activity of these neurons and thus improve their social behavior.
In an earlier paper, they had already shown that, on a chemical level, so-called "germ-free" mice have significantly higher levels of the hormone corticosterone (the analog of what we think of as the "stress hormone" in humans: cortisol) than mice with healthy microbiomes.
"By altering the mouse's microbiome, we were able to change levels of corticosterone: less microbiome means more stress hormone," explained one of the post docs involved in the project.
So, what was it about the gut bacteria—or lack thereof—that was causing increased corticosterone levels in the first place? To address this, the team conducted fecal transplants from mice with normal gut microbiota into these germ-free mice lacking a gut microbiome. These mice then showed decreased corticosterone levels and more normal social behavior.
More intriguing still, the researchers identified a specific bacterial species that did this: namely Enterococcus faecalis. Germ-free mice that were colonized with E. faecalis showed improved social behaviors and lowered corticosterone levels.
The mechanisms through which E. faecalis is able to mediate this improvement will be the subject of future research.
From a therapeutic viewpoint, it still seems that eating a wide variety of different whole foods that help to feed a diverse and robust microbiome is probably the most practical way-- at least at the moment-- to respond to this growing body of research suggesting that keeping our gut microbes happy and healthy is a key component of health-- and maybe also happiness.
The Japanese are taught from childhood to eat 30 different foods each day. And while the intended goal might originally have been to ensure adequate intake of the various vitamins and minerals required for good health, more and more we are realizing that much of the benefit of such variety is actually enjoyed by the little critters in our intestines. More on this in a future post though!
Access the original Nature paper here.