What We’ve Missed About the Gut–Brain Connection, According to Next Health Founder Dr. Shah (2026)

Dr. Shah of Next Health sits down with Dr. Steven Gundry to explore how the gut–brain connection shapes mood, inflammation, and long-term health.

By Dr. Darshan ShahFounder & CEO of Next Health

Dec. 31, 2025 12:05 PM PT

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For years, I’ve treated patients whose symptoms didn’t fit neatly into any one diagnosis. Brain fog with no neurological cause, autoimmune flares that come and go, and chronic inflammation that never fully resolves.

Over time, one pattern became impossible to ignore as a root cause of all of these symptoms: When the gut is compromised, everything else seems to follow. This critical revelation allowed me to finally “heal” these patients’ symptoms by healing their gut.

The Gut Isn’t Passively Absorbing Nutrients. It’s Strategically Running Our Nervous System.

A few weeks ago, I sat down with Dr. Steven Gundry, a heart surgeon and pioneering researcher in microbiome science whose work has transformed our understanding of gut-driven inflammation, autoimmune disease, and the gut-brain axis to discuss how deep that connection really goes and how much we’ve underestimated the gut’s influence over the brain, immune system, and even aging itself.

“The gut isn’t just digesting food,” Dr. Gundry told me. “It’s running the conversation.” That idea resonated with me. Because once you understand that the gut is not a background system but an active communicator, the entire framework of health begins to shift.

For decades, medicine treated the gut as plumbing. Important, but secondary. The real intelligence, we assumed, lived in the brain. But as Dr. Gundry explained, that hierarchy doesn’t hold up. “The microbiome is constantly communicating with the brain,” he said. “And it’s also talking to the mitochondria, which are ancient bacteria themselves.”

That detail matters. Mitochondria, the structures responsible for energy production, originated as bacteria that were absorbed into our cells millions of years ago. They still communicate in bacterial language. Which means our bodies are in constant biochemical dialogue… between microbes, mitochondria, and the brain. “It’s not that the brain controls the gut,” he said. “It’s that they’re in constant negotiation.”

The Gut Barrier Most People Don’t Realize They’re Losing

One of the most striking parts of our conversation was about the gut barrier. A structure most people have never heard of, yet depend on every day.

The barrier is made up of three layers: a mucus layer, a living microbial ecosystem, and the intestinal lining itself. “When that system breaks down,” Dr. Gundry explained, “...things that were never meant to enter your bloodstream begin to leak through.”

What makes this especially dangerous is how quietly it can happen. “People can live for decades with a compromised gut barrier and feel mostly fine,” he said. “Until one day, they don’t.” By the time symptoms like autoimmune disease, metabolic dysfunction, or chronic inflammation appear, the process has often been underway for years.

Gut health hacks for a longer life

Why Probiotics Rarely Work on Their Own

One of the most common misconceptions around gut health is that probiotics are the solution. “You can swallow all the probiotics you want,” explained Dr. Gundry, “but unless you give them what they need to eat, they’ll die.” Beneficial bacteria require fuel… primarily in the form of fermentable fibers and the metabolic byproducts of fermentation. Without those, probiotics simply pass through. “That’s why people say probiotics ‘don’t work,’” he said. “They’re planting seeds in concrete.” True gut repair requires rebuilding the environment… not just adding organisms.

The Power of Short-Chain Fatty Acids

One of the most important discoveries in microbiome science involves short-chain fatty acids like butyrate and acetate. “These compounds are not optional,” Dr. Gundry said. “They’re essential.” They help maintain the gut lining, regulate inflammation, and act as communication signals between microbes and human cells.

But they don’t come from supplements. They’re produced through collaboration…when specific bacteria ferment specific fibers. “It’s an assembly line,” he explained. “If one part of the process is missing, nothing gets made.” This is why diversity matters more than perfection.

The Bacteria Everyone Is Talking About

One microbe that continues to draw attention is Akkermansia mucinophila, a bacterium that lives in the mucus layer of the gut. “It eats mucus,” Dr. Gundry said, “but that actually stimulates your body to produce more. It’s a renewal process.” Even more surprising: bacteria don’t need to be alive to be beneficial. “Dead bacteria still talk,” he explained. “They send signals that tell the rest of the microbiome what’s happening.” That insight can help reframe how we think about probiotic supplements. And biology itself.

The Gut–Brain Connection Runs Deeper Than We Thought

We often think of serotonin as a brain chemical, but the reality is that most of it is produced in the gut. That realization has major implications for mental health. “If antidepressants worked directly on the brain,” Dr. Gundry said, “people would feel better immediately. But they don’t.” Instead, improvement takes time… suggesting that the microbiome itself is being reshaped first. “It’s not happening up here,” he said, gesturing toward his head. “It’s happening down here.”

When the Gut Drives Disease

Over decades of clinical practice, Dr. Gundry has seen a consistent pattern. “One hundred percent of my autoimmune patients have leaky gut,” he said. In many cases, addressing gut integrity, rather than suppressing the immune system, becomes the turning point.

He described patients whose autoimmune symptoms resolved after gut repair, including one woman whose severe postpartum autoimmune condition disappeared entirely once her gut healed. “She wanted another child,” he said. “She couldn’t stay on immunosuppressants. And once her gut healed, everything changed.” One of the hardest truths for patients is that healing isn’t instant. “The gut lining regenerates quickly,” Dr. Gundry said, “but rebuilding an ecosystem takes time.”

This one really hit home for me, as I also suffered from an autoimmune disorder 10 years ago, and the rheumatologists kept increasing my medication dose. It was when I healed my own gut that the autoimmune illness simply vanished, and I was able to stop taking the immune suppressants. This may not work for everyone, but more often than not, I have seen it be very helpful.

Where to Begin

For most people, meaningful progress can begin with a few foundational habits. Eating a wider variety of plant foods, incorporating fermented foods when the body tolerates them, supporting sleep and nervous system regulation, and avoiding extremely restrictive diets unless medically necessary.

Healing is about creating the right conditions for the body to recover, and then the body (and the gut) knows exactly what it needs to do.

The Bigger Picture

What stood out most in the conversation was the realization that longevity isn’t just about optimization, but more about resilience. Populations that live the longest tend to share one trait: diverse, adaptable microbiomes. “They’re not doing biohacks,” Dr. Gundry said. “They’re supporting systems that know how to take care of themselves.” And that may be the most important takeaway of all. “We’re not trying to live forever,” he added. “We’re trying to live well while we’re here.”