Interview with Kiran Krishnan, Chief Microbiologist on Gut Health Hacks, Leaky Gut, Immunity, PCOS, and SIBO

Gut health has become one of those phrases that is everywhere, yet the practical questions remain confusing. What is actually happening in the gut? Is a probiotic worth taking? What is the difference between a probiotic, prebiotic, postbiotic, and synbiotic? Why do stress, antibiotics, C-sections, PCOS, endometriosis, insulin resistance, and SIBO keep appearing in the same conversation?

Dr. Thais Aliabadi and Mary Alice Haney sat down with Chief Microbiologist Kiran Krishnan and Just Thrive Co-Founder and CEO Tina Anderson to get past the buzzwords and into the science. The core message was simple: gut symptoms such as bloating, gas, constipation, cramps, and diarrhea may be signals of a bigger shift in the microbiome. They are not always isolated digestive complaints.

Table of Contents

• Gut Health Is About More Than Bloating
• How to Think About Probiotics and Prebiotics
• Early Life, Birth, and Building a Child’s Microbiome
• Antibiotics, Stress, and the Microbiome
• PCOS, Endometriosis, Hormones, and the Gut
• SIBO: Why More Bacteria Is Not Always Better
• A Science-First Approach to Gut Health
• Our Biggest Gut Health Takeaways

Gut Health Is About More Than Bloating

Why has gut health become such a major conversation in medicine and wellness?

Kiran Krishnan: The microbiome may be one of the biggest developments in biological and medical research in a long time. It is changing how we understand how the body works and where chronic disease processes may begin.

For a long time, gut health was reduced to indigestion, bloating, cramping, gas, and bathroom habits. Those symptoms matter, but we should think of them as potential warning lights. They can be signs that the ecosystem inside the digestive tract is not functioning as it should.

The gut microbiome is not one uniform population of bacteria. Different regions of the mouth, stomach, small intestine, and large intestine have different microbial ecosystems. Each region has its own environment and its own role. A healthy intervention should not simply flood the system with microbes. It should support the beneficial organisms already living there while helping reduce dysfunctional overgrowth.

What changed our understanding of the microbiome?

Kiran Krishnan: Until roughly 15 to 20 years ago, microbiome research relied heavily on growing microbes from stool samples in a lab. That approach only identified a small fraction of what was actually there because many gut organisms are obligate anaerobes. Oxygen is toxic to them, so they cannot be easily grown using older techniques.

DNA sequencing changed the entire picture. Scientists could identify microbial DNA without needing to culture every organism. Suddenly, we could see a vastly more diverse and complex ecosystem than we had understood before.

This matters because the old probiotic model was often based on taking a few familiar bacterial types and delivering extremely high counts in the hope that they would overwhelm the system. But if those organisms do not survive stomach acid, bile salts, and the journey through the small intestine, the number printed on the bottle may not tell us much about what reaches the intended site alive.

How to Think About Probiotics and Prebiotics

What makes a true probiotic?

Kiran Krishnan: A probiotic is a live microorganism that, when administered in an adequate amount, provides a health benefit to the host. There are three key pieces in that definition:

• It must be alive.
• It must be delivered at an amount supported by evidence.
• It must demonstrate a meaningful health benefit.

If an organism is no longer alive, it falls into a different category, often called a postbiotic. Bigger numbers are not automatically better either. We need clinical data that supports the dose and the function of a particular strain or combination.

Why do spore-based probiotics come up so often in this discussion?

Kiran Krishnan: We were interested in what we might call nature’s probiotic. Historically, humans had much more contact with the natural environment. We ate roots and tubers, handled food directly from the ground, and had far more exposure to environmental microbes.

Most environmental microbes should be destroyed by stomach acid. That gastric barrier is important. But a group called Bacillus endospores has a special protective form that helps it survive harsh conditions. In spore form, the microbes are dormant and protected by a tough outer shell. Once they reach the intestines and encounter the appropriate environment, they can become active.

These microbes may also participate in quorum sensing, which is essentially microbial communication. They can read signals in the local microbial environment and respond to what is happening around them. The objective is not simply adding bacteria, but helping shift the balance away from dysfunctional organisms and toward beneficial resident microbes.

What is a prebiotic, and why does it matter?

Kiran Krishnan: Think of a prebiotic as food for beneficial microbes. Many important organisms in the large intestine rely on complex carbohydrates called oligosaccharides. We cannot digest these structures ourselves, and many microbes cannot use them either. That specificity is part of what makes them useful.

Breast milk is the perfect example. It contains many prebiotic compounds that are not primarily there to feed the baby directly. They exist to feed and establish the baby’s microbiome. In that sense, the microbiome’s first food is a prebiotic.

A probiotic and prebiotic that work well together are called a synbiotic. The right organisms and the right microbial food can be complementary. But not every probiotic and prebiotic combination is compatible, which is why we should not assume that combining random products will always be beneficial.

Early Life, Birth, and Building a Child’s Microbiome

Does birth method influence a baby’s microbiome?

Kiran Krishnan: Yes. A vaginal birth exposes a baby to an important early inoculum of maternal microbes, including bifidobacteria and lactobacilli. These initial organisms help establish the early microbial environment.

With a C-section, the earliest microbes in the baby’s gut may more closely resemble organisms from the skin and respiratory tract of people in the room. Research discussed in our conversation associates C-section birth with different microbiome development and, later, elevated risks involving obesity, metabolic disease, asthma, allergies, and autoimmune conditions.

But this is not about inducing panic or guilt. C-sections can be medically necessary and lifesaving. The question is how we support microbiome development afterward.

What can support a baby’s microbiome after a C-section?

Kiran Krishnan: Breastfeeding is a powerful support when possible. Breast milk contains microbes, immune components, and a remarkable range of prebiotic compounds. Even small amounts may be valuable, and skin-to-skin contact, closeness, and normal family microbial exposure all play a role.

When babies begin eating solid foods, diversity and fiber become increasingly important. Mashed vegetables and other fiber-containing first foods can help support microbial development. By around age three and a half, the microbiome begins to resemble an adult microbiome more closely.

For families navigating formula feeding or C-section birth, we should work with a pediatrician to make individualized decisions. Kiran also discussed researched infant probiotics containing Bifidobacterium infantis, an organism that has an important early role in the infant microbiome.

Are we too clean with children?

Kiran Krishnan: We should use common sense, but modern life has increasingly separated us from environmental microbial exposure. A Finnish allergy study compared communities in Finland and nearby Russia and found that more sterilized indoor environments were associated with higher allergy rates.

Researchers later introduced outdoor soil exposure in some daycare settings and followed children over time. The children with regular soil exposure had lower rates of allergies, asthma, and viral infections in the findings discussed.

We are not telling anyone to abandon hygiene or skip necessary medical care. We are saying that healthy outdoor play, contact with nature, and reasonable exposure to the world around us can be part of a child’s healthy development.

Antibiotics, Stress, and the Microbiome

How much can antibiotics affect the gut?

Kiran Krishnan: Antibiotics are essential in many situations. We absolutely need them for bacterial infections such as strep, and this conversation is not anti-antibiotic. The issue is that antibiotics do not distinguish perfectly between harmful and beneficial bacteria in the gut.

During the time an oral antibiotic is present in the digestive tract, it can sharply reduce microbial populations. The concern becomes what grows back first. When lactic-acid-producing organisms decline, the gut environment can become less acidic. That can create an opening for fungi or opportunistic organisms that thrive under different conditions.

One course of antibiotics may alter the microbiome for a long time. The conversation also highlighted research suggesting that microbiome changes can occur among people sharing a household with someone taking antibiotics. Microbes are not isolated to one person. We live in a shared microbial environment.

What is the practical approach to probiotics and prebiotics during antibiotics?

Kiran Krishnan: In the framework we discussed, start a compatible probiotic and prebiotic on day one of antibiotics when appropriate, ideally under medical guidance. A spore-based probiotic may function in the presence of antibiotics, while the prebiotic provides food for beneficial keystone organisms.

The suggested strategy was to continue the probiotic and prebiotic for at least three times the duration of the antibiotic course. For a 10-day antibiotic prescription, that means supporting the microbiome for approximately 30 days afterward.

When spacing is practical, take the probiotic and prebiotic a couple of hours before or after the antibiotic. But if life makes that impossible, the discussion noted that taking them at the same time may still be beneficial. The most important point is never to delay, stop, or modify prescribed antibiotics without speaking to the prescribing clinician.

Can stress disrupt the gut as much as an antibiotic?

Kiran Krishnan: Stress is one of the largest factors influencing adult gut flora. Repeated small stressors throughout the day can alter the microbiome. Think about the person who is cut off in traffic, arrives late, opens stressful emails, and goes from one pressured meeting to another. Those repeated stress surges add up.

Many opportunistic microbes can read host stress signals, including cortisol, epinephrine, and norepinephrine. When the body is stressed, these organisms may have an opportunity to increase their activity. This can become a cycle: stress contributes to dysbiosis and intestinal permeability, and a disrupted microbiome may lower the threshold for the next stress response.

Gut support therefore cannot be only about supplements. Stress management is part of gut health management. We need to consider sleep, recovery, daily pressure, and the pace of modern life.

PCOS, Endometriosis, Hormones, and the Gut

Can gut dysbiosis influence PCOS, hormone balance, and chronic inflammation?

Kiran Krishnan: This is a complex relationship, and it is not always possible to separate a single cause from a single effect. But dysbiosis can be an important root contributor to hormone dysregulation and inflammation.

PCOS is commonly associated with insulin resistance, androgen-related hormone imbalance, and estrogen metabolism issues. For a deeper patient-focused discussion of lifestyle support for insulin resistance and PCOS, see our guide to PCOS diet and exercise.

In the gut, there is a collection of microbes sometimes called the estrobolome. These organisms participate in estrogen metabolism and recycling. Estrogen is processed by the liver and sent back to the gut for removal. A diverse microbiome can help support that process.

When microbial diversity declines, certain organisms may deconjugate estrogen, removing the chemical structure that allows it to be cleared. The estrogen may then be reabsorbed instead of eliminated. That is one proposed route through which gut dysbiosis may contribute to hormone dysregulation.

This is especially relevant when we consider conditions connected to chronic inflammation. PCOS and endometriosis are not digestive diagnoses, but many people with these conditions also struggle with bloating, pain, bowel changes, fatigue, and inflammation. Learn more about the symptoms, diagnosis, and individualized treatment options for endometriosis.

Does the gut cause PCOS or endometriosis?

Kiran Krishnan: We should resist overly simple answers. These conditions develop over time and involve genetics, hormones, inflammation, metabolism, and environmental factors. But the gut may be an important contributor because it affects intestinal permeability, inflammation, liver burden, estrogen handling, and insulin resistance.

Rather than asking whether the gut is the only cause, a better question may be: is the gut a modifiable part of the larger picture? For many people, the answer is likely yes. Gut support should complement, not replace, appropriate gynecologic, endocrine, fertility, or gastrointestinal care.

SIBO: Why More Bacteria Is Not Always Better

What is SIBO and why does it cause so many symptoms?

Kiran Krishnan: SIBO stands for small intestinal bacterial overgrowth. In simple terms, it involves microbes growing in the small intestine where they should not be present in high numbers.

Low stomach acid can be a contributor. Acid-suppressing medications, frequent antacid use, and stress may reduce the stomach’s ability to act as a barrier. We swallow enormous numbers of oral microbes through saliva every day. If they survive the stomach when they normally would not, some can reach the small intestine and begin to overgrow.

Those organisms can contribute to small intestinal permeability and inflammation. They may slow intestinal movement, which leaves food sitting longer in the small intestine. Then microbes ferment that food, contributing to gas, bloating, distension, cramps, nausea, and bowel disruption.

The inflammation can also affect the liver through the portal system. Since the liver plays such an important role in hormone metabolism and detoxification processes, this may create another connection between SIBO, inflammation, and hormonal symptoms.

Why are people with SIBO often told to avoid probiotics?

Kiran Krishnan: The reasoning is understandable. If there is already an overgrowth of microbes in the small intestine, adding large quantities of conventional probiotic bacteria may worsen bloating or inflammatory symptoms for some people.

That does not mean every probiotic behaves the same way. In the approach discussed, spore-based probiotics may be used differently because they are intended to support gut barrier function and use quorum sensing to compete with dysfunctional bacteria. But SIBO is highly individual, and treatment should be guided by a qualified clinician.

Prebiotics require extra caution in the early phase of SIBO. Fermentable prebiotic compounds may be fermented too early in the small intestine, worsening gas and distension. Once motility and symptoms improve, a person may gradually reintroduce small amounts of prebiotic support to feed beneficial organisms in the large intestine.

What other areas matter in a SIBO plan?

Kiran Krishnan: We need to think beyond the small intestine itself. The conversation highlighted three important considerations:

• Stomach acid support: Stress management and nutrient status, including magnesium and zinc, may be relevant. Any consideration of hydrochloric acid supplementation should be supervised by a clinician.
• Liver support: The liver may be under substantial pressure when endotoxins and inflammation are elevated.
• Oral health: If problematic gram-negative bacteria are abundant in the mouth, they may be repeatedly introduced into the digestive tract through saliva.

SIBO is not a situation for random supplement stacking. It deserves a thoughtful plan, careful symptom monitoring, and clinical support.

A Science-First Approach to Gut Health

Why did Tina Anderson build a gut health company?

Tina Anderson: My husband and I came from the pharmaceutical industry, where we saw how often healthcare focused on managing symptoms without digging deeply enough into the root cause. Pharmaceuticals can be indispensable in acute and emergency settings, but chronic conditions need more than symptom control.

When the Human Microbiome Project and emerging research made the importance of the gut clearer, we wanted to build a science-backed approach around strains with the ability to survive and function where they are needed. The goal was to create a new category in the probiotic space, not simply repeat what had already been done.

We should be skeptical of products that rely on marketing alone. A probiotic should be evaluated by its specific strain, survival characteristics, clinical data, dose, and relevance to the person taking it.

What is the simplest daily supplement routine discussed?

Tina Anderson: For the product approach discussed, the probiotic is taken once daily with food, ideally at the largest meal. The time of day is less important than taking it consistently with food.

The prebiotic can be spread through the day, whether in powder or capsule form. It is useful to think of the probiotic as the living organisms and the prebiotic as fertilizer for the garden. The point is to nourish the beneficial microbes over time.

We should remember that gut health is not a quick fix. People may first notice changes in bowel regularity, gas, bloating, or digestion. Over time, they may also notice changes involving energy, sleep, and how they feel day to day. But every body is different, and persistent or severe symptoms deserve medical evaluation.

Our Biggest Gut Health Takeaways

If we had to make this conversation practical, where would we start?

Dr. A and Mary Alice: We would start with a few basics and keep them consistent. Gut health does not need to become a complicated full-time job.

• Eat for microbial diversity: Include a variety of fiber-containing foods as tolerated.
• Take antibiotics seriously but without fear: Use them when medically necessary and discuss gut support with the prescriber.
• Prioritize stress management: Daily stress is not separate from physical health.
• Get outside: Reasonable contact with nature and outdoor play matters, especially for children.
• Do not self-treat SIBO, PCOS, or endometriosis: These conditions require individualized care.
• Choose supplements critically: Look for evidence, strain specificity, survival, and a clear reason for using the product.

We are walking, talking ecosystems. That is not meant to be scary. It is actually empowering. When we care for our microbiome, we may be supporting digestion, immunity, inflammation, metabolism, hormone balance, and resilience all at once.

For more expert conversations on PCOS, endometriosis, menopause, fertility, and women’s health advocacy, explore the SHE MD podcast library.

Medical note: This conversation is educational and does not replace personalized medical advice. Consult a qualified healthcare professional before starting supplements, changing medication, or treating symptoms such as persistent pain, severe bloating, unexplained weight changes, irregular bleeding, or suspected SIBO.

Gut Health FAQs

What is the difference between a probiotic and a prebiotic?

A probiotic is a live microorganism that has a demonstrated health benefit when used in an appropriate amount. A prebiotic is a compound, often a complex carbohydrate, that feeds beneficial microbes already in the gut.

Can we take probiotics while taking antibiotics?

The approach discussed uses a compatible probiotic and prebiotic during antibiotics, preferably spaced a couple of hours from the antibiotic when practical. However, individual needs vary, so we should confirm the plan with the prescribing clinician.

Can stress cause gut problems?

Yes. Repeated stress can alter the gut microbiome and contribute to intestinal permeability. Gut disruption can then make the body more reactive to stress, creating a reinforcing cycle.

Should people with SIBO take prebiotics?

Not necessarily at first. Prebiotics may worsen bloating and distension when they are fermented in the small intestine. A clinician can help determine when and how to reintroduce them gradually.

Is gut health connected to PCOS?

Gut dysbiosis may contribute to inflammation, insulin resistance, intestinal permeability, liver burden, and altered hormone metabolism, all of which can be relevant in PCOS. It is one important part of a broader, individualized treatment plan.