The gut does more than digest food—it plays a major role in your mood, sleep, and even motivation to exercise. Scientists now believe it may also be linked to diseases like Parkinson’s and long COVID.
This complex connection between the gut and the brain is known as the gut-brain axis, and researchers are discovering just how much our digestive system influences overall health.
How the Gut and Brain Communicate
The gut and brain are in constant communication through the vagus nerve, which connects them directly, and through molecules released into the bloodstream by gut bacteria and immune cells. This system helps the brain understand what’s happening inside the body, a process called interoception.
While scientists have a good understanding of how we sense the outside world through vision, hearing, and touch, they are still uncovering how the body senses internal conditions like hunger, blood sugar levels, and fatigue.
Many of these signals come from the gut. Bacteria in our intestines produce molecules that affect the brain, influencing mood, energy levels, and even cognitive function. When this communication breaks down, it can lead to health problems.
Long COVID and the Vagus Nerve
One of the most intriguing discoveries about the gut-brain connection involves long COVID. Scientists at Stanford Medicine, led by Dr. Christoph Thaiss and Dr. Maayan Levy, found that people with long COVID have lower levels of serotonin, a molecule that affects mood, memory, and sleep.
Their study on mice showed that long COVID reduces activity in the vagus nerve, leading to memory and cognitive issues. When the mice were given fluoxetine (Prozac), an antidepressant that boosts serotonin levels, their cognitive function improved.
This suggests that long COVID may affect the brain through the gut rather than directly infecting brain cells. Researchers are now exploring whether electrical stimulation of the vagus nerve—a treatment already used for epilepsy and depression—could help with long COVID symptoms.
The Gut’s Role in Mental Health and Motivation
The gut microbiome—the collection of bacteria and other microorganisms in our digestive system—also plays a major role in mental health. Studies have shown that transferring gut bacteria from people with depression into animals can cause them to exhibit signs of depression and anxiety.
Similarly, in a 2022 study, Thaiss and his team found that certain gut bacteria influence how much mice enjoy exercise. Mice with specific microbes were more likely to run on exercise wheels, while those without them were less active. When the researchers swapped their gut bacteria, their motivation to exercise changed as well.
The reason? These gut bacteria produce fatty acid molecules that stimulate nerves in the gut, which then signal the brain to release dopamine—the “feel-good” chemical. This suggests that our gut microbes could play a role in whether we feel motivated to move.
Stress also affects the gut microbiome. People under chronic stress tend to develop imbalances in their gut bacteria, which can make them more prone to inflammation and mental health issues. High-fiber and fermented foods have been shown to improve gut health, which in turn may help with overall well-being.
Is Parkinson’s Disease Linked to the Gut?
Scientists are now investigating whether Parkinson’s disease, a brain disorder that affects movement, might actually begin in the gut. People with Parkinson’s often experience digestive issues like constipation years before they show movement symptoms. Researchers have also found that Parkinson’s patients have different gut bacteria compared to healthy individuals.
A 2024 Harvard study found that damage to the upper digestive tract, such as from acid reflux or ulcers, can increase the risk of Parkinson’s years later. The disease is marked by clumps of misfolded proteins called Lewy bodies in the brain, but researchers suspect these abnormal proteins might start forming in the gut before traveling to the brain via the vagus nerve.
Dr. Ami Bhatt and Dr. Kathleen Poston at Stanford Medicine are studying how gut bacteria and the immune system might trigger Parkinson’s. Their team is comparing stool and blood samples from Parkinson’s patients and their spouses to understand how the disease affects the gut microbiome.
The Gut’s “Second Brain”
The gut has its own nervous system, called the enteric nervous system, which contains over 100 million neurons—more than any part of the body outside the brain. This system controls digestion and can even function independently of the brain.
Dr. Julia Kaltschmidt and her team at Stanford Medicine are studying how gut neurons regulate digestion. In a recent study, they found that activating specific neurons can speed up food movement through the digestive tract. Their goal is to develop a “gut pacemaker” that could help treat chronic constipation, which is common in aging and certain diseases.
Why This Research Matters
These discoveries highlight just how important the gut is for both physical and mental health. The gut-brain connection influences everything from mood and memory to motivation and disease risk.
Although scientists are still learning how to improve brain function by targeting the gut, we already know that maintaining a healthy gut microbiome is beneficial. Diets rich in fiber and fermented foods can promote good bacteria, reduce inflammation, and potentially improve overall well-being.
In the future, therapies that focus on gut health—whether through diet, medication, or nerve stimulation—could be used to treat conditions like depression, Parkinson’s, and long COVID. As research continues, the gut may prove to be a key player in keeping both the body and mind healthy.
If you care about Parkinson’s disease, please read studies that Vitamin B may slow down cognitive decline, and Mediterranean diet could help lower risk of Parkinson’s.
For more health information, please see recent studies about how wheat gluten might be influencing our brain health, and Olive oil: a daily dose for better brain health.
The research findings can be found in Neuron.
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