Episode 27 · The Wellness Path Podcast · 23 February 2026 · Hosted by Dr. Vic Manzo, DC
Your baby’s gut contains over 500 million neurons — more nerve cells than their entire spinal cord — and between 90 and 95 percent of the body’s serotonin is produced there rather than in the brain. In this episode, Dr. Vic Manzo explains how the infant microbiome shapes emotional regulation, sleep, immune function and cognitive development, why the first 1,000 days matter most, and what parents can do at any stage to support it.
What You’ll Learn in This Episode
- Two brains, one body — why the gut contains more nerve cells than the entire spinal cord
- The vagus nerve highway — 80 to 90% of signals travel from the gut up to the brain, not the other way around
- Serotonin and GABA — 90 to 95% of the body’s serotonin is produced in the gut
- The HPA axis and anxiety — why germ-free environments in early life are linked to hyperactive stress responses
- Antibiotic debt — how early antibiotic use alters gut-brain communication for months or years
- The first 1,000 days — why conception to the second birthday is the most critical window for neurological programming
The Gut-Brain Connection: A Neurological Ladder
- The Architect (Microbiome) — the foundational builder of the body’s internal environment. A healthy gut produces butyrate, a short-chain fatty acid that protects the blood-brain barrier and reduces neural inflammation.
- The Messenger (Vagus Nerve) — the high-speed highway connecting gut and brain, transmitting calming signals like GABA and serotonin to regulate mood and sleep.
- The Shield (Immune System) — a healthy gut trains the immune system to distinguish a real threat from a safe environment, reducing allergies and sensitivities.
- The Top Floor (Cognitive Function) — healthy gut-brain communication influences language development and complex problem-solving.
Full Episode Transcript
What if I told you that the single most powerful predictor when it comes to your child’s IQ, their emotional regulation, their anxiety levels, their ability to focus in school and life, wasn’t genetics. It wasn’t the school. And it wasn’t even the parenting strategies that you’re using right now. What if it lived in their diaper?
Now I’m not being dramatic here. I’m being very scientifically precise. And in the next 20 to 25 minutes I’m going to walk you through the research that has fundamentally changed the way I look at every single child who walks into our office and our practice.
Welcome to the show. My name is Dr. Vic Manzo. For those who don’t know, I’m a neuro-focused pediatric chiropractor, and this is where we go deep into where neuroscience meets the real world for healing for the children you love most.
So in today’s episode, The Second Brain in the Diaper: how the infant microbiome dictates future IQ and emotional regulation. And I promise you, by the end of this you’re never going to look at a colicky baby, a tantrum-prone toddler, or even a child who struggles in school the same way ever again.
Two Brains, One Body
There are really two brains in one body, and this discovery has changed a lot of things. When you think of the brain as the neurological master control — the brain, nervous system, spinal cord — it’s the master controller of everything in the body. This is why, from a chiropractic perspective, I always tell people go chiropractic first. Because if you’re looking at a system and you have something showing up, you want to figure out whether the control systems are working well first. You get there, and then you can look at other things on top of it.
The whole nervous system, the most important organ in the entire body — I should change that and say the most sensitive — is encased in bone. Your brain and your spinal cord.
But one of the most interesting discoveries that has come out in the last 30 years in neuroscience is that you have a second brain, and it lives in your gut. It’s gotten out there in the last five to ten years, but this is known as the enteric nervous system. That’s the technical term. It contains over 500 million neurons. Your spinal cord has only about 100 million. Your gut has more nerve cells than your entire spinal column. That’s pretty deep.
Here’s where it gets remarkable for infants specifically. At birth the gut is almost sterile. It’s a blank canvas. Within hours of being born the microbes start to colonize it. If you go through a vaginal birth, that is the first layer of probiotics being put into the gut. The conditions under which they thrive or perish determine everything.
And what’s interesting — this is why chiropractic again, control of everything — the nervous system also helps tell it where it needs to go. This is your house, this is where you’re going to live. The programming, and how that second brain communicates with the first one, is literally determined by whether this bacteria thrives or not.
This is not a metaphor. This is not wellness fluff. There are researchers at institutions like Harvard, the Karolinska Institute, and University College Cork publishing in top-tier journals like Nature, Cell and Neuron. This is published research that supports a lot of this.
The Vagus Nerve Highway
We know the gut and the brain communicate with each other — known as the gut-brain axis. A lot of this happens through the vagus nerve. We even have studies showing that when you look at someone who has Parkinson’s, the Lewy bodies that happen in the brain — they found that actually starts in the gut first. It goes two ways.
So whenever I work with an ADHD kiddo, you have to focus on gut and brain, because the gut can fire up the brain and the brain can fire up the gut. They work with each other.
The vagus nerve is critical for pretty much all health in humans. It has immunomodulating functions — a fancy word for helping control and work with the immune system. It also has effects on hormones, and it works with a family of molecules called short-chain fatty acids.
The infant microbiome — the collection of bacteria, viruses and fungi living in that little gut — is the operator and controller of that highway. It influences and affects the brain in so many ways.
In my practice I talk about something I call the brake pedal. It’s the parasympathetic nervous system. About 70 to 80 percent of that brake pedal system is based on the vagus nerve. It’s the longest cranial nerve in the body. It goes from the brain all the way down to the top of the prostate in males or the top of the bladder in a woman. That’s a very, very long nerve. It’s known as the tenth cranial nerve.
About 80 to 90 percent of the signals travelling on the vagus nerve go from the gut up to the brain, not the other way around. So your baby’s gut is constantly sending reports upstairs. It’s constantly asking: what kind of environment is this? Are we safe? Are we stressed? Are we nourished? And the microbiome is writing those reports.
I want you to understand the microbiome is intelligent. It is literally telling your brain what’s going on in the environment from a bacterial perspective — because of what we’re eating, what’s in the system. It’s one of the ways the brain knows, because the brain needs to know everything it possibly can so it can orchestrate and help you thrive in every situation.
Serotonin, GABA and the Chemistry of Calm
When we have a healthy, diverse microbiome, it produces neurotransmitters. Around 90 to 95 percent of the body’s serotonin is produced in the gut, not in the brain. This includes precursors for GABA — a neurotransmitter that diminishes excitatory neurons in the brain and helps it calm. That’s the brain’s primary calming chemical.
Serotonin influences mood, emotional regulation and sleep, and in the developing infant it is actively sculpting neural circuits. This is critical.
Let me slow this down, because I want it to land. The bacteria in your baby’s gut are helping to build the brain. They are not just passengers. They are the architects.
This is why, when I work with couples looking to get pregnant — whether they have fertility issues or they’re just planning — the first thing I recommend is: are we aiming for a vaginal birth? Great. Number two, find out what the probiotic balance is in your vaginal canal. There’s testing you can do. The goal is to give yourself four to six months to balance that out.
Why do I recommend that? Because the first line of your child’s gut bacteria comes when they pass through the vaginal canal. If you have a C-section, that’s the hospital’s bacteria instead. So you understand what’s lining it right off the bat.
Short-Chain Fatty Acids and Butyrate
Research has looked at beneficial species like Bifidobacterium and Lactobacillus. These ferment dietary fibre and produce short-chain fatty acids — SCFAs. The main ones create butyrate, propionate and acetate.
Butyrate is remarkable. I try to get butyrate in as much as I can. I’m a big brain guy — I like taking things that help keep my brain healthy and sharp. Butyrate is one of the things that can cross the blood-brain barrier. It reduces neural inflammation, it supports the integrity of the blood-brain barrier itself so it gets stronger and doesn’t let things through, and the kicker: it epigenetically regulates gene expression in neurons. It actually influences which genes in brain cells get turned on and off. I can’t tell you how powerful that is.
A study at UC Davis and several European cohort studies have found correlations between early-life microbiome diversity, SCFA production, and cognitive outcomes — including language development, problem-solving ability, and scores on developmental assessments. We’re not talking about a minor effect. We’re talking about foundational influence.
The HPA Axis and Emotional Regulation
Now I want to get into the HPA axis, because this is what I see every day in clinic. I see kids that are overstimulated, having major emotional outbursts, going from zero to a hundred before you know it. This is nervous system dysregulation.
The HPA axis is the hypothalamic-pituitary-adrenal axis. It’s our stress response — how the body fires up stress. It’s a beautiful system that works wonders when it doesn’t get overused. It’s one of the laws of the body: what you abuse, you lose.
This controls cortisol. Cortisol is not a bad thing — it’s the most potent anti-inflammatory in the world. But it’s not good when there’s too much. This controls our fight-or-flight mechanisms, and in infants this is extremely sensitive to gut signals.
Animal studies in the 2000s, since replicated and expanded into human research, showed that germ-free animals — animals raised with no gut microbiome — had a hyperactive HPA axis. They produced excessive cortisol in response to stress. They showed anxiety-like behaviours. And critically, the window to correct this was narrow: early colonisation with healthy microbes could normalise the HPA axis, while late intervention had much less impact.
Now, my question — which I didn’t look into — is what were they doing for intervention? Because I believe there are things you can still do. You can change your gut around; it’s always changing. But in the beginning it grows quick and fast.
This maps to what I see clinically. In children with dysbiotic gut environments — meaning an imbalance of good and bad bacteria and other organisms — what we normally see is hypervigilance, emotional dysregulation, difficulty with transitions, and sensory sensitivities. These are a lot of the kids I see. I took two years off practice and I’m seeing this ten times more than before.
We have been calling these behavioural issues. What we should have been asking is: what’s happening in the gut?
The First 1,000 Days
Scientists talk about the first 1,000 days — from conception through approximately the second birthday — as the most critical window for human neurological development. The microbiome’s influence is front and centre in that window.
Mode of delivery is one of the most significant determinants of early microbiome composition. Infants born vaginally are seeded with Lactobacillus species from the birth canal. Infants born by C-section are instead initially colonised primarily by skin and hospital-environment microbes — a profile that looks very different and has been associated with higher rates of allergies, asthma and obesity, with emerging data suggesting differences in cognitive and behavioural outcomes.
I also think there are neurological factors, because with a C-section the skull doesn’t get that compression through the birth canal. I believe that’s part of why you’ll see more asthma and breathing issues related to that. But I’ll stick to what I researched for this episode.
Breastfeeding is the next major architect. Human breast milk contains over 200 distinct oligosaccharides — complex sugars the infant cannot even digest. They’re there specifically to feed Bifidobacterium infantis, a keystone probiotic species that produces protective compounds, helps train the immune system, and supports the gut-brain axis. Formula simply cannot replicate this.
This is why I’m very big on breastfeeding duration being consistent. Studies show babies who are breastfed — and we’re not even talking about mom’s diet or supplements, just breastfeeding in general — show better cognitive and emotional outcomes overall. When someone asks how long we should breastfeed, I say a year is a minimum and two years is a beautiful sweet spot.
Antibiotic Debt
There’s also research showing that antibiotic exposure matters. This is why on my intake form I ask: have they had ear infections? Have they been on antibiotics? How many doses, and at what ages?
Antibiotics are sometimes absolutely necessary. I get that. I’m not anti-medicine — I want to be very clear about that. But the research is clear that broad-spectrum antibiotic use can dramatically reduce microbiome diversity. And the thing about antibiotics is it’s not “I’m off it now, my gut can heal, it’ll come back.” This persists for months, and sometimes years.
I was an antibiotic baby growing up. I had multiple ear infections. I almost died at four and a half years old with bacterial meningitis — imagine the antibiotics I had to take. I had so much antibiotics before the age of five. I cannot tell you how long it took to heal my gut. I didn’t start my journey until I was 19 or 20. I had severe Candida and didn’t even know that was what it was. It took years upon years. Now at 42 my gut has been fully healed. But it has taken so long.
One study looked at a single course of antibiotics in the first six months of life and found it was associated with measurable alterations in gut-brain communication markers.
What I See in Clinic
I want to share the typical child I’m seeing in my office. This is not one specific child — I have to protect privacy — it’s a composite. I see a pattern time and time again, and I document these patterns so I know the trends, and then we measure outcomes.
You see a three or four-year-old who is bright and excited. You see the clarity in their eyes, that beautiful light children have because they’re pure. But there’s a struggle. They have meltdowns that seem disproportionate. They’re not sleeping well. They have chronic constipation or loose stools. Their immune system is constantly challenged. They may have speech delays, or they didn’t crawl when they roughly should have.
The rules we still follow are neurological — crawling around eight to ten months, walking by a year, language milestones at two, three, four and so forth.
They may have seen paediatricians, specialists, sometimes therapists, and everyone’s treating one piece of the puzzle in isolation. No one’s having the conversation: how was the pregnancy and how was birth? No one’s asking about antibiotic history. No one’s asking how mom’s microbiome was during pregnancy. No one’s mapping out the gut-brain axis to ask what the nervous system is actually receiving from that enteric environment.
That’s what we do differently. When I look at a child I’m looking at every facet. How are their primitive reflexes, because those tell me whether the brain developed in sequence — retained primitive reflexes are a sign a nervous system has not developed through its proper sequence. I look at cranial mechanisms, because the birthing process places normal stress on the cranium. I look at vagal tone, because low vagal tone — which is the majority of what I see — plays a huge role in the gut-brain highway. And I look at the gut and everything connected to it.
The nervous system doesn’t just stop at the skull. It goes all the way down to the microbiome. When you address all of it — structural, neurological, nutritional, microbiome — that’s when you see children really transform.
What This Looks Like in Babies
What you normally see is excessive crying or colic that doesn’t resolve. Difficulty breastfeeding or taking a bottle due to oral motor tension — a lot of people go straight to tongue and lip ties, and I’m not saying that isn’t a cause, it’s an organic issue that’s probably adding to this. But there are cranial and neurological factors affecting these things. The nerves control the tongue. The nerves control certain reflexes. We need to look at that first.
Constipation, or green mucousy stools indicating gut inflammation. Poor sleep consolidation, meaning the baby cannot stay in sleep cycles. Hypertonicity or hypotonicity of the body, specifically the neck, usually turning to one side. Excessive startle response. Difficulty being put down and calmed.
These are not normal baby things, and they’re not things you want to wait out. They don’t grow out of them. This is the nervous system telling you it needs support, and the microbiome and vagal tone are usually the signs.
The Autonomic Picture
The autonomic nervous system is the parasympathetic and sympathetic — I call the sympathetic the gas pedal and the parasympathetic the brake pedal. The more we hit the gas pedal, the more imbalance we create in the gut too, because stress affects the gut. If the nervous system is stuck in stress, we create more dysbiosis and weaken the gut.
You Are Not Helpless
Knowledge without action is just anxiety. I don’t want to leave you anxious — I want you to leave empowered.
Whether you have a newborn at home, a toddler, you’re pregnant right now, you’re thinking about having a family, or your kids are six, seven, eight, ten, twelve or teenagers — all of these pillars can be optimised. Nothing is stuck. Just because you maybe didn’t do the first 1,000 days, that’s okay. You can still change things over time. If that weren’t true my gut would never have healed.
If you’re pregnant, know that your microbiome is transferred to your baby. Prioritising probiotic-rich foods — fermented vegetables, kefir, yoghurt, kimchi — and prebiotic fibres during pregnancy is one of the most powerful gifts you can give your child before they’re born. I like soil-based probiotics; they’re the best at getting through to the colon. I’ve been recommending them for 15 years.
If you’ve had a C-section, this is not a life sentence for your child. There’s a lot we can do, including from a cranial perspective. It doesn’t replace a vaginal birth, but we can get as close as we can with cranial work. There’s also research on vaginal seeding, where you introduce vaginal flora to the newborn’s skin and mouth after a C-section birth. Discuss that with your midwife or OB.
Probiotic supplementation for the infant is critical. Strains like Lactobacillus rhamnosus GG and Bifidobacterium infantis are the two that are meaningfully supportive. If you’re breastfeeding you can express into a bottle and mix it in. If you’re formula feeding you can add it there.
Be antibiotic-thoughtful. Minimise use where possible. If there’s a necessity, do it — but use the minimum you can.
Chiropractic care. This is my world. We do nervous system first, because I want to see whether correcting the vagus nerve, getting the nervous system running, taking the stress response down, and regulating the gas pedal and brake pedal takes care of things. Usually it helps. If it doesn’t, we go to the next level. Everything’s layers.
We look at cranial work — this is not craniosacral therapy, which is something different and which I’m a huge fan of. We look at primitive reflexes, because if those are still active it puts your child’s nervous system in a hyperactive stress state. There is massive stress firing in the background. When we resolve those reflexes over time, it takes that stress out and allows them to develop the way they were designed to.
Feed the gut well. The gut is not just where food goes — it’s a neurological organ. What you feed it literally shapes the brain. As you start solids, typically around six months, diversity is everything. Expose the microbiome to as many different plant fibres and age-appropriate fermented foods as you can. A program I love and follow for my own kids is Solid Starts — they make it simple, with images, and help your child get exposed to a hundred foods in the first six months of eating solids.
Omega-3s. If you’re breastfeeding, take them. DHA is structurally essential for brain development and it supports the integrity of the gut lining. When the lining is intact, gut-brain signals are cleaner. When it’s compromised, research calls this intestinal permeability — leaky gut, in other words — and it lets things into the system that shouldn’t be there.
The Science Summary
The gut-brain axis is bi-directional communication between the enteric nervous system and the central nervous system, mediated primarily through the vagus nerve, immune signals and microbiome metabolites.
The microbiome in the first 1,000 days is a primary programmer for the HPA axis — the body’s stress response. Dysbiosis in this window has been associated with increased anxiety, emotional dysregulation and cognitive differences.
Short-chain fatty acids produced by beneficial gut bacteria cross the blood-brain barrier, decrease neuroinflammation, and influence epigenetic expression in the brain. They are literally writing instructions for brain cells.
Around 90 to 95 percent of serotonin is produced in the gut. Mode of delivery, breastfeeding, and early antibiotic exposure are the three biggest modifiable factors in early microbiome development.
As a chiropractor, addressing the vagus nerve, the tone of the nervous system, cranial mechanisms and primitive reflexes is critical.
What I Want You to Walk Away Knowing
Your child’s brain is being built right now. Not in the classroom. Not ten years from now. Right now — in the microbiome ecosystem of their gut, in signals travelling up and down the vagus nerve. Every nap, every feeding, every interaction.
The decisions you make in this window — the foods, the care, the providers, the awareness of the gut, the support of your child’s nervous system — are not small decisions. They are long-term investments in your child’s health.
And the most important thing I’ll leave you with: it is never too late to start supporting the nervous system. It is never too late to start supporting the gut. The brain is plastic. It’s always changing. The microbiome shifts and can change too. The nervous system is the biggest thing to regulate first — when we address that first, it starts the healing process and takes the stress off.
If this sparked something in you, and you’re sitting there thinking you want someone to look at your child through this lens, reach out. This is exactly what I do. If you’re not in the Knoxville, Maryville or Morristown area, reach out to us anyway — we have connections to people we can get you to.
And if you know a parent who needs to hear this today — a new mom, a parent struggling with their toddler’s meltdowns, someone navigating a child with developmental challenges — share the episode. You might be the reason they finally find the right answers.
Thank you for being here. Thank you for caring this deeply about the next generation. I look forward to seeing you in the next episode.
Map Your Child’s Gut-Brain Axis
If you want someone to look at your child through this lens, that is exactly what we do. The NeuroFoundation Assessment is $197 and includes a hands-on functional neurological exam, your child’s NeuroSync Efficiency Index score, and a full report of findings reviewed with Dr. Vic.
Call or text (865) 214-7438, or book online at thewellnesspath.janeapp.com. The Wellness Path serves families across Knoxville, Maryville and Morristown, Tennessee.