COMMENTARY

Microbes and Mental Health: The Link Between Biome and Brain

Emily Deans, MD

Disclosures

March 04, 2016

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Hi. I'm Dr Emily Deans. I am an instructor of psychiatry at Harvard Medical School, and I am here today as part of our ongoing monthly video series on diet, lifestyle, and mental health for Medscape Psychiatry.

Today I am going to be talking about the microbiome. You may be wondering what the microbiome—the 37-100 trillion little beasties in our guts—has to do with the brain and psychiatric illness. Emerging research has shown that there is a profound link between the gut and the brain.

We tend to think of lifestyle affecting the brain via the hypothalamic-pituitary-adrenal (HPA) axis. Chronic stress or chronic derangements of the HPA axis, along with an underlying genetic vulnerability to psychiatric illness, causes psychiatric symptoms. We know that these symptoms are associated with neuroinflammation and elevation of certain inflammatory serum cytokines.

What does that have to do with our gut? Well, as it turns out, everything. The gut microbiome is a key component of our immune system and mediates a lot of the communication along our HPA axis. The gut microbiome has three different ways of communicating with the brain: hormonally, via the immune system, and via direct mechanisms. Some of the microorganisms in your gut actually release neurotransmitters that speak to your brain via the vagus nerve.[1,2,3]

Animal studies have shown that you can change a rodent's behavior just by changing the microbiome. There are numerous ways to do this, including probiotics, antibiotics, prebiotics (fibers that feed the microbiota), and fecal transplants.

In human studies, probiotics have been shown to reduce negative thinking in healthy human subjects[4]and reduce anxiety in subjects undergoing cancer treatment.[5] One dramatic but rather small study showed that the administration of probiotics to babies significantly reduced the development of autism or ADHD 13 years later.[6]

Right now, researchers are working on strains of so-called "psychobiotics" that we might be using as part of our armamentarium in the future to fight mental illness.

What can we do right now? We know that poor sleep, poor diet, chronic stress, and too much alcohol adversely affect our microbiome. The effect is almost immediate. You can have a 40% reduction in the diversity of your microbiome within 10-14 days of eating a highly processed food diet.

It is believed that this dietary interaction with the microbiome may explain why people who eat a traditional whole-foods diet are up to 40% more resilient to stress and developing mental illness than those who eat a processed Western foods diet.

Avoiding processed foods and reinforcing good sleep habits are strong evidence-based recommendations that you as a clinician can make today that can help your patients and their microbiomes at the same time.

If your patients have irritable bowel syndrome, there is now a large body of evidence showing that probiotics can help not only their irritable bowel but possibly anxiety and associated depression as well.

Every month, new and exciting studies emerge about the microbiome and mental health. We will be sure to stay on top of the evidence and report back to you here at Medscape Psychiatry. If you want to dive deeper, many of the references are open access and are great reads for you. Thank you and have a great day.

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