If you’re stressed before a presentation, you’ll probably have a jumpy stomach. That’s the brain influencing the gut. And if you eat something disagreeable, you’ll probably see a decline in your mood. That’s the gut influencing the brain.
These are just two examples of the gut-brain axis. What happens to one influences the other, and vice versa.
For smoother digestion, lower inflammation, and a brighter mental state, you must simultaneously care for the gut and brain. Keep reading to learn how.
What Is the Gut-Brain Axis?
The gut-brain axis describes the bidirectional relationship between[*]:
- The gut (and microbes colonizing the gut)
- The central nervous system (which includes the brain and spinal cord)
Let’s review how the gut and brain interconnect.
#1: Nerves and neurons
The central nervous system is like your CEO, but it’s not the only hub of bodily control. The gut is also lined with millions of neurons that comprise the enteric nervous system.
The enteric nervous system regulates digestion, blood flow, and other functions. This “second brain” connects to the actual brain via the vagus nerve.
Proper vagal tone is crucial for gut-brain health. Unsurprisingly, people with irritable bowel syndrome (IBS) and Crohn’s disease (inflammatory bowel disease) have impaired vagal nerve function.[*]
#2: Gut microbes and neurotransmitters
You’ve probably heard of neurotransmitters. These chemical messengers regulate mood, digestion, sleep, and many other functions.
Take serotonin, a neurotransmitter famous for influencing mood. More than 90% of your body’s serotonin is produced in the gut.[*]
Along with mood, serotonin also regulates gut motility.[*] (A serotonin imbalance may cause diarrhea or constipation.) That’s why drugs that act on serotonin, like SSRIs, are indicated for irritable bowel syndrome (IBS).
Relevant here: a person’s serotonin balance (and balance of other neurotransmitters) depends on the trillions of bacteria, yeast, and viruses colonizing the gut. Yes, your gut microbiome helps make neurotransmitters.
How does an optimal gut microbiome look? It depends on the person, but supplementing with certain microbes (called probiotics) has been shown to improve digestion, lower inflammation, and boost mood in animals and humans.[*]
#3: Immune health
The gut houses about 70-80% of all immune cells.[*] So when something disturbs your digestive system—a virus, trigger food, stress, etc.—immune activity (inflammation) soon follows.
And when inflammation is present, depression may be present too.[*][*] The most direct evidence for this theory comes from a study you wouldn’t sign up for.
In the experiment, researchers injected twenty men with either Salmonella endotoxin (yes, Salmonella) or saline solution.[*] The Salmonella group showed higher levels of inflammation in response to the poison and exhibited symptoms of anxiety and depression.
IBS and Other Conditions Linked to the Gut-Brain Axis
IBS is often a label for chronic stomach pain and irregular bowel habits, but there are diagnostic criteria for a formal diagnosis. Since up to 20% of the global population suffers these symptoms, it pays to explore what causes them.[*]
The symptoms aren’t just gut symptoms. For instance, over 80% of IBS patients also suffer from anxiety or depression.[*]
But what causes what? Do IBS symptoms cause anxiety or does anxiety cause IBS symptoms?
Likely both. For example, stress fires up the immune system and can cause “leaky gut,” a state of gut permeability that leads to GI symptoms.[*]
We also know that inflammatory cytokines can cross the blood-brain barrier and derail your mood. Remember the salmonella study?[*]
It’s a bidirectional relationship. You need to mind both sides of the equation.
Researchers also look to the gut-brain axis to explain neurological disorders, including:
- Multiple sclerosis. MS patients have altered microbiomes, and probiotics have been shown to improve symptoms.[*]
- Alzheimer’s disease. Stool samples from Alzheimer’s patients show increased numbers of Bacteroidetes, a bacteria linked to increased inflammation.[*]
- Schizophrenia. When mice received stool transplants from schizophrenia patients, those mice developed schizophrenic behavior.[*]
To be clear, the research is still in its infancy. But we don’t need a PhD in the microbiome to live in ways that support the gut-brain axis.
Eating to Support Gut-Brain Health
To support your gut and brain, focus on avoiding inflammatory foods. The more you limit inflammation, the better your gut-brain axis will function.
Eliminating refined sugar is a smart first step. Excess sugar consumption leads to obesity (an inflammatory state)[*] and promotes a pro-inflammatory microbiome.[*]
You should also lance vegetable oils like soybean oil, peanut oil, and sunflower oil. Like sugar, excess omega-6 consumption has been linked to chronic inflammation.[*]
So what should you eat? Simple: eat unprocessed, whole foods that agree with you!
If a food is causing symptoms—GI or otherwise—it’s probably causing inflammation. Eliminate the food and try it again in about a month.
What about fiber? For folks with healthy guts, higher fiber intakes are usually better.
Fiber feeds beneficial bacteria, but—depending on the situation—fiber can also feed pathogenic bacteria in the gut. Consequently, reducing fiber intake reduced GI symptoms in IBS patients.[*]
Experiment with carbs and fiber to see what best suits your digestion and cognition. Some folks do best with minimal carbs (aka, Keto), but others don’t.
Other Ways to Support a Healthy Gut-Brain Axis
Supporting your gut-brain axis is a holistic endeavor. Eating healthy is just one piece of the puzzle.
Here are some other puzzle pieces:
- Adequate sleep. Sleep disruptions negatively impact the gut microbiome.[*]
- Stress management. Stress releases corticotropin-releasing hormone, which increases intestinal permeability (leaky gut).[*]
- Regular exercise. Moderate exercise promotes better cognition and a more diverse gut microbiome.[*][*]
- Omega-3 fatty acids. Higher omega-3 intakes have been linked to healthier gut bacteria and reduced depression risk.[*][*]
- Probiotics. Studies show that taking probiotics may improve mood and GI symptoms.[*][*]
- Sun exposure. Natural sun exposure fosters anti-inflammatory gut bacteria.[*]
You don’t need to be perfect in every area, but perhaps you can make one or two adjustments. Even a tiny improvement in your gut-brain axis can significantly improve your quality of life.