You're not who you think you are.

Gut feelings and decision making.

Did you make a decision recently? Did you look at lots of different options, weigh them up and then decide what to do? If so did you wonder what things might be influencing this process? All good so far but did you consider that your Firmicutes and Bacteroidetes might be influencing you too? What was your gut saying?

I am an ecosystem, as are we all, our understandings about this expand all the time. I remember saying to people several years ago that “I don’t know who I am any more and I’m not even sure who is saying this!” That’s because I have been following the research on the Human microbiome for years now and said research has sparked a revolution in how we think about ourselves.

Each of us is a community of billions of cells and most of these aren’t human ones. Fungi, viruses, bacteriophages, archaea and bacteria are all over us and in many places inside us too. Mouth, eyes, lungs, intestines and so on are colonised by a diversity of microbes and they have ways of transmitting information. The flow of information along the Vagus nerve has been known for some time now and more recently we’ve discovered others. For example NOD2 (nucleotide oligomerization domain) receptors on the hypothalamus reacting to muropeptides (the building blocks of the bacterial cell wall). The Hypothalamus manages bodily functions such as body temperature, reproduction, hunger and thirst. The NOD2 receptors detect variations in bacterial activity and the hypothalamus adapts appetite and body temperature according to the information received.

So what, when and how much I eat is partly decided by the my gut microbiome. Even more fun is that my decision making is also influenced by my good old microbiome, so we wind our way back to your Firmicutes and Bacteroidetes. Hilke Plassmann and her colleagues from the Paris Brain Institute and the University of Bonn show that changes in gut microbiota can influence our sensitivity to fairness and how we treat others. They did this study using the Ultimatum game, this involves 2 people, A and B. A has some money and B knows how much. A makes a proposition to B about how to share the money, 50/50 or something else. B can then decide to accept the offer or refuse it, if they refuse it both players walk away with nothing.

The skew on this study was doing the Ultimatum test twice. The second time after half the study population had received pro and prebiotics for 7 weeks. These people changed their responses in the second round of Ultimatum game, the ‘control’ people changed little or nothing. The treated people started to show a greater sensitivity to fairness, becoming more inclined to reject any proposition that was away from 50/50.

Rejecting virtually all offers that are not 50/50 is seen as being irrational because both parties lose everything. OK, maybe, but for virtually all of our history except the very recent 8000 years or so sharing fairly was how we survived maintained cohesive groups without which an individual couldn’t survive. So in this context either proposing or accepting an unequal share-out is irrational and will led to social breakdown. Hunter-gatherer groups have quite sophisticated social mechanisms that ensure fair sharing.

OK, so far so good so let’s roll in some other studies about our gut microbiomes. People eating what we can call a modern diet have a less-diverse gut microbiome compared to hunter-gatherers. The change seems to have occurred after the adoption of cereal agriculture thousands of years ago. It also changed or oral microbiomes and encouraged Streptococcus mutans, the major culprit behind tooth decay, well done us! Sugar disrupts the microbiome and eliminates protection against obesity, patients with type 2 diabetes have an altered gut microbiota, major disturbances occur in the gut microbiome of patients suffering from heart disease. children with ASD harbor distinct and less diverse gut bacterial composition. The studies go on and on, the importance of a healthy microbiome cannot be understated.

Just a few bits more! A few years ago researchers were hoping to identify a ‘standard microbiome’. Then it would be possible to devise diets that led people to this ‘ideal state’. That idea has been abandonned because we each have microbiomes that are highly individualised. The different areas, mouth, lungs, gut etc are interconnected and changes to the diversity or types of bacteria in one part changes the others. This most likely happens through the immune system which is itself affected by changes to the microbiome.

Our personal microbiomes are relatively stable but alter with seasonal changes, diet, disease and stress. Stop the stress, change the diet, and the microbiome returns to how it was, as is the case when we stop taking antibiotics. These results come from short-term studies ranging from a few weeks to years or decades. Other studies looking at longer timescales like the transition from hunter-gathering to farming show that microbiomes evolve and that diet is the most important factor driving this. We’ve got more teeth rotting Streptococcus mutans because we eat much, much more sugar than our deep ancestors.

I mentioned that stress causes changes to the gut microbiome, discrimination is a form of stress and often pushes people to ‘comfort eating’. This tends to mean eating more unhealthy sweet foods, increased cravings for unhealthy foods, especially sweet foods, this causes alterations in the bidirectional communication between the brain and the gut microbiome. “This occurs via inflammatory processes in the brain-gut microbiome system involved in dysregulations of glutamatergic signalling and modulation of the frontal-striatal circuits.” So according to the study discrimination, racial or otherwise can be a cause of obesity.

Our microbiomes are negatively impacted by ultra-processed foods, by pesticides, by the so-called forever molecules and by nano and micro plastic particles. The changes involve the change from a healthy microbiome with a good diversity that helps us digest a healthy and varied diet to ones in which certain microbes come to dominate. Take xanthan gum as an example, it’s widely used in processed foods and we eat a lot of it. One microbe, a bacterium from the family Ruminococcaceae, breaks down the carbohydrates in xanthan gum and then the fragments are further digested by the Ruminococcaceae bacterium. Widespread consumption of the xanthum gum seems to actively alter our gut microbiomes and this is not a good thing. Stop eating it and the microbiome will find it’s original, individual, state again.

So, in the end, who is influencing my decision making? Lot’s of factors but one which we haven’t counted in are the food, agricultural and industrial systems. They are producing stuff that causes changes in our microbiomes, often through inflammations, and our microbiomes have an influence on what decisions we make. Moving away from these industries and their products and getting back to healthy diets that encourage better microbiome diversity would, it seems, encourage us to treat each other more fairly. If all goes well maybe lead us towards creating more equitable and just societies. As discrimination would be absent from these societies that should help with our current obesity epidemic. Everything is connected to everything else, let’s make those connections good ones!