Stress, the Immune System, and the Microbiome

As we discussed yesterday, it seems likely that our interior bugs are, in a very real sense, “the boss of us.” Even when this idea was relatively novel, a article by John F. Cryan and Timothy G. Dinan outlined the hopes that appeared on the horizon for treating eating disorders and obesity by way of the gut-brain axis.

From the start, connections with stress response were identified. At the time, they wrote:

Accumulating data now indicate that the gut microbiota also communicates with the CNS — possibly through neural, endocrine and immune pathways — and thereby influences brain function and behavior.

Dr. Emeran Mayer, who has been investigating the human microbiome for 35 years, says:

The hypothesis that microorganisms in our intestine have somehow managed to hack into our reward system, enabling them to make us crave for foods that are good for them, is intriguing. If this concept turns out to be correct, one could speculate that as a by-product of this food-seeking strategy, alterations in mood may be a consequence…

Credentialed as both gastroenterologist and neuroscientist, Dr. Mayer directs UCLA’s Oppenheimer Family Center for the Neurobiology of Stress. Via the Center’s Ingestive Behaviors and Obesity Program, he seeks to learn whether, and how, the gut microbiome affects eating behavior in obesity and weight loss. Important questions need to be asked about hedonic value and the effects of hyperpalatable foods.

The Center team studies the impact of stress as expressed through sex, race and culture, and the possibility that brain structure plays a role. Brain-gut interaction is suspected of taking a major part in three particular areas: autism, chronic pain and obesity. Dr. Mayer says:

The question driving our research is: why do overweight people continue obesogenic behaviors even though they deconstruct their lives on multiple levels?[…] 1.4 billion people are overweight. Are all of those brains broken?

In this worldview, the role of family genetics is recognized but occupies a backseat. Also acknowledged is the tendency of bariatric surgery to cause appetite reduction and changes in food preferences. One of the Center’s openly proclaimed goals is to reproduce those brain changes without surgical intervention.

The researchers collaborate with UCLA pediatricians to study food preferences, eating habits and behavior, and brain activity in children. Then, there is what Dr. Mayer calls the chicken and egg question: “Do abnormalities in the gut influence the brain, or do abnormalities in the brain influence the gut?”

Two things are for sure. Microbes and their metabolites send out signals, and our bodies are riddled with receptors where those signals land. In the gut, they activate vagus nerve endings which are compared to an information highway to the brain.

This particularly disturbing quotation concerns stress hormones:

Animal studies have shown that the release of these chemicals can change the gene expression profile of the bacteria in the gut, causing their virulence genes to be up-regulated.

In other words, when the adrenal glands secrete adrenaline, and nerve fibers release norepinephrine, some gut bacteria are stimulated to become more infective and pathogenic. When the chemicals hit the receptors the micro-organisms develop superpowers that enable them to inhibit or evade the person’s immune response and make all sorts of other aggressive moves.

By one estimate, two-thirds of the human immune system resides in the gut. As we have seen, certain bacteria prefer a substance that we can’t ourselves digest, and turn resistant starch into butyrate, which feeds our T cells, which reinforce the gut lining and strengthen the immune system.

Other bacteria are not so cooperative. What if some of the feelings we interpret as stress and anxiety are caused by the tension of the inner battle between our intelligent consciousness, which wants to do what is best for us, and the constant nagging of trillions of organisms that have some contrary agenda in mind?

Your responses and feedback are welcome!

Source: “Mind-altering microorganisms: the impact of the gut microbiota on brain and behaviour,”, October 2012
Source: “A Hijacked Brain and a Tongue Held Hostage,”, 08/07/14
Source: “From the Desk of Emeran A. Mayer, MD,”, Spring 2014
Source: “Why we feel emotions in our guts, and what microbes have to do with it,”, 07/08/16
Source: “9 Weird Things Killing Your Gut,”, 04/08/14
Photo credit: gianky via Visualhunt/CC BY

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About Dr. Robert A. Pretlow

Dr. Robert A. Pretlow is a pediatrician and childhood obesity specialist. He has been researching and spreading awareness on the childhood obesity epidemic in the US for more than a decade.
You can contact Dr. Pretlow at:


Dr. Pretlow’s invited presentation at the American Society of Animal Science 2020 Conference
What’s Causing Obesity in Companion Animals and What Can We Do About It

Dr. Pretlow’s invited presentation at the World Obesity Federation 2019 Conference:
Food/Eating Addiction and the Displacement Mechanism

Dr. Pretlow’s Multi-Center Clinical Trial Kick-off Speech 2018:
Obesity: Tackling the Root Cause

Dr. Pretlow’s 2017 Workshop on
Treatment of Obesity Using the Addiction Model

Dr. Pretlow’s invited presentation for
TEC and UNC 2016

Dr. Pretlow’s invited presentation at the 2015 Obesity Summit in London, UK.

Dr. Pretlow’s invited keynote at the 2014 European Childhood Obesity Group Congress in Salzburg, Austria.

Dr. Pretlow’s presentation at the 2013 European Congress on Obesity in Liverpool, UK.

Dr. Pretlow’s presentation at the 2011 International Conference on Childhood Obesity in Lisbon, Portugal.

Dr. Pretlow’s presentation at the 2010 Uniting Against Childhood Obesity Conference in Houston, TX.

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