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Your Gut and Your Resistance to Stress

Changing your diet could make you more resilient.

Could your gut be affecting your mental health?

The science is young, but we see the connection to the gut in some psychiatric conditions like depression and PTSD, through chronic low-grade inflammation.

You've probably heard the term "microbiome" floating around. The microbiome is some 500 to 800 species that live on and inside the human body, and are most populous in the large intestine or colon. Stress and a diet of fewer kinds of plants has likely cut the diversity of the microbiome in most of us.

The Yanomami, hunter-gatherers in the upper Amazon, have the most diverse microbiome known today.

According to the “hygiene hypothesis,” when young children aren’t exposed to enough microorganisms they end up with too few regulatory T cells, which normally function to suppress the activity of other cells in the immune system.

With too few of these traffic cops, the theory goes, we end up with chronic low-grade inflammation. The body's immune response to stress may go awry generally, Dr. Christopher Lowry, Associate Professor in the Department of Integrative Physiology at the University of Colorado Boulder, explained in a webinar broadcast by the Brain & Behavior Foundation.

Both stress and immune dysfunction has been tied to mental ill-health. People with autism, depression and PTSD all tend to have fewer regulatory T cells. People with PTSD also have a higher risk of autoimmune disorders.

In one study Lowry mentioned, Marines at boot camp with higher concentrations of C-reactive protein (CRP) in the blood, a sign of inflammation, were more likely to develop PTSD symptoms after deployment.

The frontier is to find the specific microorganisms needed to protect against unhealthy immune activity. In a study with colleagues in South Africa, Lowry’s team found, for example, that among a group of people in South Africa exposed to trauma, certain microorganisms in the gut were linked to lower rates of PTSD.

The Value of “Orange Slime”

In the early 1970s, the British researcher John Stanford and his colleagues noticed that vaccines against leprosy were most effective in an area around Lake Kyoga in Uganda. “The shores of the lake were lined with “orange slime,” Lowry said. The slime turned out to be M. vaccae, a close relative of the species, M. leprae, that causes leprosy.

To test how M. vaccae affects the stress response, Lowry conducted a mouse experiment, injecting the bug into mice just before subjecting them to stress--a bullying, dominant male. It turned out that the injections made the mice more likely to likely to chase or attack the dominant male rather than turn up their tails, a subordinate response. In humans, a “passive or subordinate response during trauma [is]associated with an increased risk for PTSD later on,” he noted.

Without the injections, the stressed mice experienced increases in interleukin-6, a pro-inflammatory immune molecule that also increases in people when they are depressed.

Can people with psychiatric conditions help themselves by trying to reduce inflammation through diet? Lowry says yes. The more different types of plants you eat, the higher your gut microbiome diversity is likely to be. Drinking at least one alcoholic drink a week also promotes diversity and eating fermented foods like yoghurt and kombucha may help. One tip: Eating a hamburger leads to a surge in inflammation but adding a slice of avocado suppresses it. Exercise and sleep are also important, he said.