How Your Gut Immune System Influences Your Mental Health

New research sheds light on a hidden part of the gut-brain connection.

Reviewed by Gary Drevitch

You’ve probably already heard that your immune system is key to your health. For example, people with an overactive immune system (e.g. chronic inflammation) or an underactive immune system (e.g. immunodeficiency) are at much higher risk for developing serious diseases. However, immunity is a much bigger deal than just a defense against microbes. We now know that it directly affects our brains and changes the way we interact with the world.

Now consider that up to 70% of our immune cells actually live in the gut. Why is this the case? One of the most important functions of our immune system is to interpret messages from the outside world for our bodies and our brains. It is also tasked with keeping out the things that might harm our bodies, and letting in those that are good for us. The gut represents one of the biggest interfaces between the inside of our bodies and our environment. It makes sense that our immune system has set up its largest base of operations in this location.

Our billions of gut immune cells have a difficult task. They have to convert information from the outside world into signals that our bodies can understand. Many of these messages are sent directly to our brains. How does this work? Every day when we eat, our digested food comes into contact with the gut lining. Our gut immune cells sample and learn from this food and share this message with the rest of the body. Additionally, these cells learn from the gut microbiome, the collection of trillions of microbes that live inside our gut. The combination of data from our food and microbes is captured by the gut immune systems and shuttled towards our brains in two major routes.

First, information from the gut immune system can be loaded into the bloodstream, where it can enter the brain through the blood-brain barrier. Immune signals can also reach the brain by way of peripheral nerves like the vagus nerve. On entering the brain, these messages can have a variety of effects. For example, if there is too much inflammation in the gut immune system, inflammatory immune signals may reach the central nervous system and alter brain function. This unhealthy inflammatory cascade has been linked to conditions like depression and anxiety. In fact, drugs targeting this very system have shown a positive effect in some types of depression.

Increasing evidence also suggests that the local communication between our gut microbes and gut immune system is a major driving force in health and disease. Recent research demonstrates the link between conditions like anxiety and depression and alterations in our gut microbiome. And while we’ve known that the gut microbiome plays a major role in shaping our immune systems, we now understand that the opposite is also true. Our gut immune cells appear to both keep out bad bugs and nurture the good microbes that are key to our physical and mental wellbeing.

So, what are the steps you can take to improve your gut immune system today? First, you need to appreciate that “boosting” immunity is a bad plan. Instead, you should seek a more balanced immune function. This can be achieved by eating more whole foods, and avoiding highly processed foods like refined carbohydrates. Consuming a range of phytonutrient-rich foods may also help. These include teas, cruciferous vegetables, mushrooms, and dark leafy green plants. You can also support better immune function by using stress-lowering interventions, getting adequate exercise, and prioritizing sleep.

Another way to promote better gut immunity is by supporting a healthy gut microbiome. Basic steps for looking after the gut microbiome include eating a variety of plant phytonutrients, getting enough fiber, and avoiding unnecessary antibiotics. Finally, eating fermented foods like kimchi and sauerkraut may help populate the gut with the right balance of microbes.

Modern science has progressively revealed that our cognition, including our mental health, is a reflection of multiple physiological processes. Among these, we’re beginning to see that our immune system plays an outsized role. This insight grants us the ability to consider novel interventions for mental health conditions. By prioritizing the health of our immunity—and especially the gut immune system—we may be able to expand the toolkit for people at risk for, or already experiencing, mental health conditions.