The Gut-Brain Axis Explained Simply: How Your Gut Affects Your Anxiety

At the time I was waking up with that feeling. Not fear exactly. More like a low-grade hum — a tightness right under my sternum that had no reason to be there. My life was fine. My apartment in Kraków was fine. I had Luna curling up against my legs and Moon, my cat, doing what cats do (absolutely nothing, with great conviction).

But my gut was not fine.

I didn’t know those two things were connected. I thought my stomach problems — the bloating after every meal, the nausea on stressful mornings, the way coffee would send me into a spiral — were a separate, boring digestive inconvenience. Not the same story as my anxiety.

Then I got my bloodwork done.

CRP is your C-reactive protein — the inflammation marker. Mine was at 8.5. My doctor said we should watch this. I started changing what I ate — slowly, cautiously, going keto Mediterranean almost by accident, because cutting out bread seemed to help both the bloating and the hum. Within four months, CRP had dropped to 1.2.

And the hum? Almost gone.

What the gut-brain axis actually is

Think of your brain and your gut as two old friends who text constantly — but one of them is much more talkative than the other.

Your gut sends about 80% of the messages. Your brain only sends back 20%.

The line they use is called the vagus nerve — a long, wandering nerve that runs from your brainstem all the way down to your belly. It’s not a direct line (no “gut calling brain, please pick up”). It’s more like a shared network where signals travel constantly in both directions, interpreting everything: what you ate, whether you feel safe, whether inflammation is up, whether your microbiome is thriving or under siege.

Your gut contains roughly 100 million neurons. Scientists call it the enteric nervous system — sometimes the “second brain.” It can operate independently. But it’s in constant conversation with your actual brain, and that conversation shapes your mood, your stress response, and yes, your anxiety.

The serotonin thing nobody tells you

Everyone knows serotonin as the “happiness chemical.” What most people don’t know is where it’s actually made.

About 90% of your serotonin is produced in the gut. Not in your brain. In the lining of your intestines, manufactured largely in response to signals from your microbiome — the trillions of bacteria living in your digestive tract.

Those bacteria aren’t passive tenants. They actively produce neurotransmitters and metabolites that travel up the vagus nerve and influence how your brain functions. When your microbiome is diverse and well-fed, the chemical signals going to your brain tend to be calming. When it’s dysbiotic — disrupted by ultra-processed food, chronic stress, or antibiotics — those signals change.

This is why gut dysbiosis and anxiety so often show up together. It’s not a coincidence. It’s a highway.

What chronic inflammation does to this highway

When I got that CRP number — 8.5 — I didn’t yet understand what inflammation does to the gut-brain connection. But it’s actually straightforward once you see it.

Inflammation irritates the gut lining. A chronically inflamed gut lining becomes more permeable — this is what people call “leaky gut,” though the clinical term is increased intestinal permeability. When the lining is compromised, bacterial fragments and other molecules that should stay in the gut can slip into the bloodstream.

Your immune system sees these as threats. It mounts a response. Inflammatory cytokines flood the bloodstream — and those cytokines can cross into the brain, where they interfere with neurotransmitter production, disrupt the HPA axis (your stress hormone system), and impair the pathways that regulate mood.

Why the keto Mediterranean diet helped me

When I shifted to a keto Mediterranean approach — fatty fish, olive oil, leafy greens, eggs, fermented foods, almost no sugar or processed carbs — several things happened at once in my gut.

First, I dramatically reduced the substrates that feed inflammatory bacteria. Second, I increased omega-3 intake — especially from sardines and wild salmon — and omega-3 fatty acids are directly anti-inflammatory, reducing the cytokine production that was likely contributing to my elevated CRP. Third, I started eating more prebiotic-rich vegetables like artichoke and garlic, which feed the bacterial species associated with GABA production.

GABA is your brain’s main inhibitory neurotransmitter — the one that says calm down, it’s okay, you’re safe. You can’t take a GABA supplement and have it cross the blood-brain barrier easily. But you can feed the bacteria that help your body make it naturally.

Within weeks, my digestion stabilized. Within months, the inflammation marker dropped. And the anxiety went quiet.

What this means for your plate

You don’t need to overhaul everything at once. The gut-brain research points to a few consistent levers:

• Sardines & wild salmon — omega-3s lower the inflammatory cytokines that disrupt the gut-brain axis. Most consistent finding in the research.
• Greek yogurt & kefir — real fermented foods seed the gut with beneficial bacteria. Not probiotic capsules — actual food fermentation.
• Artichokes, garlic, leeks — prebiotic fiber feeds what’s already there. Think of it as fertilizer for your inner ecosystem.
• Extra virgin olive oil — oleocanthal acts as a natural anti-inflammatory and supports gut lining integrity.
• Walnuts — plant-based omega-3s plus polyphenols that feed Lactobacillus strains linked to reduced anxiety.
• Reduce: refined sugar & seed oils — they disrupt the microbial community your gut needs to talk clearly to your brain.

Blood sugar stability matters more than people expect. Blood sugar spikes drive cortisol spikes, which suppress the vagus nerve signal and worsen gut permeability. The reason a Mediterranean-keto hybrid works for anxiety — not just weight — is partly because it flattens that cortisol roller coaster.