Your Anxious Brain, Your Stressed Gut, and the Loop Between Them

Episode 175: Spotify | Apple Podcasts | YouTube
View transcript on Buzzsprout

One of the things clients are most surprised to learn is how often anxiety or depression shows up alongside digestive issues. IBS, constipation, reflux, bloating, food sensitivities. And usually those two things have been treated in completely separate corners. A doctor addresses the gut symptoms over here and the anxiety over there, and nobody ever connects them, even though the relationship between your mental health and your gut health is well documented and each one can make the other considerably worse.

Today we’re getting into that connection. What it actually is, what it means for you if you’re dealing with anxiety, depression, or even more general symptoms like brain fog and poor sleep, and where the popular version of this conversation tends to get oversimplified.

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What We Cover in This Episode

• How your brain and gut communicate through the vagus nerve and the gut brain axis
• The serotonin claim you’ve probably seen on Instagram, and why it’s more complicated than it sounds
• What your gut microbiome and gut permeability actually are
• What disrupts gut health, including stress, diet, and certain medications
• How to know if gut health testing is worth considering for you

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How Your Brain and Gut Talk to Each Other

Your brain and gut are in constant communication through what’s called the gut brain axis. That communication travels through several pathways, your nervous system, immune system, hormones, inflammatory signals, and your gut microbiome. One of the major physical routes is the vagus nerve, your longest cranial nerve, which begins in your brainstem and travels down through your neck, chest, and abdomen, connecting to many of your internal organs and ending in your colon.

This communication runs in both directions. Your brain sends signals down to your body, and your body sends signals back up about what’s happening internally. That’s why stress can affect your digestion so quickly. You’re about to give a presentation and suddenly you feel nauseous. You’re waiting on difficult news and you lose your appetite. You’re anxious about leaving the house and suddenly you need the bathroom.

When your nervous system detects a threat, real or imagined, it moves into fight or flight. Survival takes priority over digestion. Your stomach slows, which can bring on nausea, reflux, or that dropped feeling in your stomach, while activity in your lower digestive tract can increase, which is part of where urgency or IBS symptoms come from. When that stress response becomes chronic, those acute symptoms can become chronic symptoms too.

The same relationship runs the other way. When something isn’t functioning well in your gut, inflammation, a microbial imbalance, impaired digestion, or changes in your intestinal barrier, it sends signals upward that can influence immune activity, inflammation, and how your brain and nervous system function. An anxious brain can create a stressed out gut, and a stressed out gut can feed an anxious brain.

An anxious brain can create a stressed-out gut, and a stressed-out gut can feed an anxious brain.

The Serotonin Claim You’ve Probably Seen on Instagram

You’ve likely seen the post. Ninety percent of your serotonin is made in your gut, so if you’re anxious or depressed, you need to heal your gut. I want to clear this one up, and I’ll admit I’ve repeated a version of it myself in the past before I understood the science more fully.

The first part is true. Around ninety percent of the serotonin in your body is produced in your gastrointestinal system. What usually gets left out is that this peripheral serotonin cannot cross the blood brain barrier. Think of it as two separate pools. The serotonin in your gut is used for digestion. Your brain has to make its own supply for brain related processes. Low serotonin activity in your brain doesn’t automatically mean your gut isn’t producing enough, and gut issues don’t automatically mean you have a brain serotonin problem.

None of this means your gut has nothing to do with your mood. Your gut still influences your brain through the vagus nerve, immune and inflammatory signaling, microbial metabolites, and tryptophan metabolism, tryptophan being one of the raw materials your brain uses to make its own serotonin. The relationship is real. It’s just more layered than a quick infographic can capture, and I don’t want you walking away thinking anxiety or depression automatically means a bad microbiome, or that fixing your gut will fix your mental health on its own. Gut health is one piece of the physiological environment your brain and nervous system function in. It matters, and it is never the one explanation for why your symptoms exist.

Two Concepts Worth Understanding: Microbiome and Gut Permeability

Your digestive tract, mainly your large intestine, is home to trillions of microorganisms, bacteria, fungi, and viruses that make up your gut microbiome. Many of them are genuinely useful. They help you break down food, absorb nutrients, support immune function, aid vitamin production, protect against harmful pathogens, and produce compounds that communicate with your brain and nervous system. Like any healthy ecosystem, we want it diverse and balanced. When it becomes significantly imbalanced, that’s what’s known as dysbiosis, a general term for an imbalance in your gut microbiome, and targeted testing is what clarifies exactly what that imbalance looks like.

Research has found a clear association between differences in microbiome composition and populations struggling with anxiety, depression, chronic stress, or inflammation. In one striking set of studies, researchers transplanted gut bacteria from people with depression into germ free mice, and those mice developed more depression like behaviors than mice who received microbiota from healthy individuals. In another study, transplanting healthier microbiomes reduced depression like behaviors. Mice are not humans, and depression doesn’t live in your gut alone, but it’s compelling evidence that the microbial environment in your gut can influence behavior and brain related processes, not just digestion.

The second concept is gut permeability, sometimes called leaky gut. Your intestinal lining works like a smart filter, selectively allowing nutrients and water through while keeping bacteria and toxins contained. When that barrier isn’t functioning well, substances that normally wouldn’t cross over do, which can trigger immune activation and inflammation. That inflammation doesn’t stay isolated to your digestive tract. It travels and can affect mood, energy, cognition, sleep, and stress reactivity. Chronic stress is one of the most common causes of leaky gut.

What Gut Dysfunction Can Actually Look Like

Sometimes it’s obvious. Chronic bloating, constipation, diarrhea, reflux, abdominal discomfort, food sensitivities, irregular bowel movements, changes in appetite. If you have persistent digestive symptoms alongside anxiety or depression, your gut health is worth paying closer attention to.

What’s less obvious is that not everyone with gut dysfunction has clear digestive symptoms. Sometimes what people notice most is anxiety that improved with therapy or nervous system work but never fully lifts, or a sense of working against an unexplainable headwind even after addressing thoughts, stressors, and regulation. For others, gut imbalance can show up as low mood, brain fog, difficulty concentrating, fatigue, sleep trouble, or feeling disproportionately reactive to small stressors. I want to name clearly that every one of those symptoms could point to plenty of other things too, hormones, a nutrient deficiency, thyroid function, poor sleep, or a demanding season of life. Mental health usually isn’t one thing. A symptom rarely has one clear root cause. Gut health is simply one piece that may deserve a place in that conversation.

What Disrupts Gut Health

Chronic stress is one of the biggest contributors. Your body digests optimally in a parasympathetic, rest and digest state, and when your nervous system spends a lot of time activated instead, it changes gut motility, digestive function, inflammation, intestinal permeability, and even your microbiome composition itself. Chronic stress isn’t only what you feel emotionally. Your nervous system adds up physiological stressors too. Poor sleep, undereating, blood sugar instability, chronic pain, loneliness, overtraining, a demanding job or relationship. All of it counts toward your stress load, and stress load that runs too high will affect your gut.

Diet plays a role as well. What you regularly eat shapes which microorganisms thrive. A diverse diet with plenty of plants and fiber generally supports microbial diversity, while a diet heavier in ultra processed foods creates a different internal environment. This isn’t about food morality or a perfect diet. It’s about patterns over time and which organisms you’re feeding in abundance.

Certain medications matter too, and I want to be careful and specific here. Antibiotics affect bacteria by design, including the beneficial kind living in your gut, which is part of why mood changes in the weeks or months after a course of antibiotics aren’t unusual. Antidepressant and anti-anxiety medications are worth understanding as well, since most of your body’s serotonin lives in the gut and plays a role in intestinal movement. That’s part of why nausea, diarrhea, constipation, or appetite changes can show up when starting an antidepressant, and why emerging research suggests some antidepressants may interact with the microbiome itself. This is not a suggestion to stop any medication, and it isn’t a claim that medication is the only reason for digestive symptoms. It’s an invitation to hold both truths at once. A medication can be genuinely helping your mental health while also affecting your gut, and both of those things deserve consideration rather than being pushed aside.

Beyond that, the usual list applies. Poor sleep, being sedentary, illness, alcohol, environmental exposures, and hormonal disruptions all play a part. Rarely is it one dramatic cause. It’s a compounding effect, chronic stress plus poor sleep plus convenient food plus a round of antibiotics plus low movement plus a hard season of life, each one adding a little weight until the balance of the system shifts.

Where to Start

Start with the foundations before you start with testing. Sleep is one of the most important levers for gut health, and that doesn’t mean a perfect night every night. It means noticing where you actually have some control, even if that’s just not handing over one more hour to your phone before bed. Feeding your gut with a wider variety of plants and fiber, vegetables, fruits, legumes, whole grains, nuts, seeds, and fermented foods like yogurt, kefir, sauerkraut, or kimchi supports microbial diversity without requiring a full overhaul. Regular movement, whatever that looks like for you, supports gut motility and correlates with microbiome diversity. And ongoing nervous system regulation and stress reduction support the whole system underneath all of it.

If you’ve got the foundations reasonably dialed in and you’re still dealing with symptoms, or if you have clear GI symptoms alongside anxiety or depression, or you simply want to stop guessing and see the full picture, that’s where gut health testing becomes useful. Most comprehensive testing is done through an at home stool sample, which gives information on microbial balance, overgrowths, pathogens, digestive function, inflammation, and markers related to intestinal permeability. The test itself isn’t the intervention though. What matters is having a qualified provider look at those results alongside your symptoms, medications, health history, and stress load, and build a plan that actually fits your current capacity and life circumstances rather than a seventeen page protocol you can’t sustain.

This is exactly why our team built Regulated Health, our functional lab testing service. Our providers look at gut health as one part of a larger system, alongside your bloodwork, your nervous system, and your mental health, rather than treating it as an isolated problem.

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Three Tangible Takeaways

1. Your gut and brain are in constant, two way communication. Stress and mental health affect digestion, and what’s happening in your gut influences brain function, mood, and your nervous system.
2. Gut health is one piece of the physiological environment your brain and nervous system function in, not the single explanation for your symptoms. It’s worth putting on the table, never the whole table.
3. Start with the foundations. Sleep, diverse nourishment, movement, connection, and nervous system regulation support gut health first. If symptoms persist, targeted testing can help you stop guessing and build a more strategic plan.

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Looking for more personalized support?

• Regulated Health, functional lab testing including comprehensive gut health panels
• Regulated Living Membership, a monthly membership for nervous system healing
• RESTORE, 1:1 coaching for anxiety and depression

*Want me to talk about something specific on the podcast? Let me know HERE.

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Disclaimer: This article is for informational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or qualified mental health provider with any questions you may have regarding a medical condition.