Understanding the Mouth-Gut Connection: How Your Immune System Begins Before Swallowing

You’ve probably heard the stat tossed around that “70%–80% of your immune system lives in your gut.” And you may have nodded and moved on. But what does that actually mean? And does it start after you swallow your food… or before?

Let’s back up to the dental chair for a second.

I was chatting with one of my longtime patients (an oncologist) during her hygiene visit (yes, we discuss the world’s health debates while polishing teeth. Multitasking at its finest.)

We got on the topic of immunity, and I casually mentioned, nonchalantly, as if it were common ground, that 70–80% of the immune system lives in the gut.

She paused, tilted her head, and said,

“Well, gut immunity is mostly IgA. That’s not the same as the systemic immune response we see in cancer care, like IgG. So it doesn’t really count as protection against viruses or bacteria in the same way.”

It was a respectful, thoughtful disagreement.

And it got me thinking… THIS is exactly why conventional and functional medicine often seem like they’re speaking different languages.

Because here’s the thing: They both have a point.

---

What Is the Mouth–Gut Connection?

Before anything hits your gut, it has to get through your mouth. Think of your mouth as the front gate and your gut as the neighborhood watch (Source).

If bad bacteria sneak past the gate, your gut’s immune team has to clean up the mess, and it’s a busy job.

Your mouth and gut aren’t just physically connected, they share a continuous microbial ecosystem (Source).

That means oral bacteria don’t stay local. They can:

1. Get swallowed and affect the gut microbiome

2. Slip into your bloodstream through inflamed gums and spark systemic inflammation

3. Disrupt the mouth’s mucosal barrier and overwhelm immune defenses before digestion even starts

   
   

---

Secretory IgA: The Body’s First Line of Defense

My oncologist patient was right: IgA (Immunoglobulin A) is the star of the mucosal immune system.

It coats your mouth, gut, nose, and lungs like a security blanket, neutralizing microbes before they enter the bloodstream. It doesn’t destroy invaders like IgG might, it blocks them at the gates.

But here’s where we disagree.

Just because IgA works differently than IgG doesn’t mean it’s not vital. Without healthy IgA levels, your immune system is like a security team asleep at the front door.

Functional medicine recognizes that this front-line protection influences everything downstream, including digestion, inflammation, and even your systemic immune response.

In functional nutrition, we don’t just wait until something hits the bloodstream to care. We ask: what should have stopped this earlier?

---

Enter the GALT: Your Gut’s Full Immune Squad

Beyond IgA, your gut’s immune system includes a full tactical unit: T cells, B cells, macrophages, dendritic cells, all camping out in your GALT (Gut-Associated Lymphoid Tissue) (Source).

It’s one of the largest immune organs in your body, and yes, it’s constantly communicating with the rest of your immune system.

So that “70%–80%” number? It holds up, especially when you understand that gut immunity doesn’t end with digestion, it’s part of the whole-body defense team.

---

The Mouth-Gut Gossip Line

Here’s where it gets juicy. Your mouth and gut love to gossip. And they’re not good at keeping secrets.

When your gums are inflamed or your breath is funky, those oral bacteria don’t just stay in your mouth. You’re swallowing them constantly, and in some cases, they can sneak directly into your bloodstream through compromised gum tissue.

Yes, brushing and flossing matter. But if that’s all you’re told to do, you’re only seeing the tip of the oral health iceberg.

Gut health, stress, diet, and immune function all shape what’s happening in your mouth, every single day.

---

What Can You Do?

1. Brush and floss like you mean it – and ask your hygienist what they see in your gums.

2. Support your gut bugs with fiber, pre and probiotics, and whole foods.

3. Reduce stress – because high cortisol levels can tank your IgA.

4. Stay hydrated – saliva is full of protective enzymes, but only if you’re drinking enough.

---

Real Talk & Final Bite

You can eat close to perfect. You can floss like a hygienist-in-training. But if your gut’s not absorbing nutrients or managing inflammation, your mouth won’t get the message.

Your oral health is an extension of your immune system, not separate from it.

That patient conversation didn’t end in a winner or loser. But it reminded me how often we compartmentalize the body in conventional care.

Functional nutrition zooms out and asks: What connects all this?

And the answer often starts with what’s happening before you even take that first bite.

— Khristina Maureen

       Your Functional Nutrition Ally

---

Curious what your oral symptoms might be telling you?

Take the Free Mouth-Body Connection Quiz or Download the Free DIG Deep Starter Guide - and start connecting the dots, one smart step at a time.

If you’re tired of feeling “off,” bloated, fatigued, your labs look fine, but you don’t feel fine,

Health Root Reboot is your next move.

It’s short, smart, and helps you connect the dots without another Dr. Google spiral.