We usually think of anxiety as a bad thing. It’s a nasty negative emotion that can be so intrusive and hard to control. You can be anxious about being anxious! But actually, it is a normal and important emotion. Basically, it is the feeling that something is not right. Somewhere. Somehow. This can motivate us to determine and address whatever it is that isn’t right.
But what happens when the something that isn’t right is not something in the mind or in the environment, but in the gut (or other part of the body)? This is interoceptive anxiety.
I first got involved in studying this issue back in 1999, when a colleague in the Psychoneuroimmunology Research Society, Mark Lyte, asked me if I would collaborate on a study with him. He is a microbiologist interested in “host-microbe interactions”. “Host” means us and other animals. He had showed that stress in the host (mice in this case) can increase growth and virulence in potentially pathogenic bacteria, which could be one way stress contributes to disease susceptibility. While studying the mice he noticed the ones that had to swallow the bacteria (this was how it was given) seemed anxious, but the ones who had to swallow saline were not (Lyte 1998). No one believed it, because he could not find any explanation for how bacteria in the gut could affect behavior. Besides being anxious, the mice who got the bacteria looked exactly the same as the controls- no inflammation, or anything.
At the time, I was studying the role of the vagus nerve in immune-to-brain communication. Mark wondered if the vagus nerve might be somehow signaling the presence of the bacteria, and so did I. Long story short- we were able to show that the vagus nerve responded to the extra bacteria in the gut fairly quickly, within a few hours, and that this led to a brain activity pattern identical to both stress and anxiety (Gaykema 2004; Goehler 2007; Goehler 2008).
This was a surprise to many people, because at the time it was assumed that bacteria living in our guts are there only because it is a cozy place to live. Sure, they interact with each other, but why would they interact with us?
Now we know that we and our microbes interact in important ways, to the good and to the bad. We are symbiotic, really. To the good, microbes provide important nutrients and substances that help regulated our immune systems. To the bad, they can overgrow and out-compete “friendly“ microbes, which can lead to functional problems in the gut, and elsewhere. This is “something wrong” and this activates interoceptive pathways (sense of the condition of our bodies) that signal brain networks that function to address challenges. The feeling of interoceptive anxiety can be one result.
We have an epidemic of anxiety in our society, which is understandable from a “top down” point of view, in that our society is going through many changes and there is uncertainty in the future. But from a “bottom-up” view, we also have a highly industrialized food system that makes highly processed foods, which are low in fiber and nutrients, easy and cheap. This type of diet is just plain bad for the gut. Even though there has recently been a lot in the various media about the dangers of the Western Diet, most people are still eating it.
For many people, it can be hard to make the link between what is happening in the gut (or other parts of the body) and brain symptoms, such as anxiety. This may be important especially important for people who have disorders attributed to the brain such as Post-traumatic Stress Disorder (PTSD), generalized anxiety, addictions, even neurodegenerative diseases (Jones 2021), that can also often have gut symptoms as well. Even if top-down factors for anxiety (such as anxiolytic drugs and psychotherapy) are effective, there may residual symptoms that could be driven by interoceptive anxiety.
The idea that poor diets can be contributing to anxiety is supported by both epidemiological studies, which have correlated diet with mood, and intervention studies (though not enough of these) indicate that eating a Western Diet is associated with more anxiety and depression (Aucoin 2021, Melguizo-Ibáñez 2023; Alexatou 2026), and that switching people with mood disorders to a Mediterranean type diet improves symptoms (Jacka 2017; Esgunoglu 2022).
Fortunately there is more better information becoming available regarding what, actually is a “good diet”. In particular, diets with plenty of fiber attract and nourish the microbes that keep our guts healthy, and improve interactions between the gut and brain.
So it seems that the alarming level of anxiety in our society may well follow from top down psychological experiences interacting with bottom-up interoceptive factors. When people are struggling with symptoms of anxiety, they should also think about their diets, and get more fiber!