Jessica Finlay: Why your microbiome may matter more than DNA for your lifelong health

Gabriela Rocha Sales — Thu, 24 Jul 2025 14:16:32 +0000

Jessica Finlay: Why your microbiome may matter more than DNA for your lifelong health Gabriela Rocha Sales Thu, 07/24/2025 - 08:16

Pulled from Big Think, webpage: (https://bigthink.com/books/microbiome-master-key/) on 7/24/25 at 8:18am.

Text copied for department archival purposes.

Article by Jasna Hodžić

Key Takeaways

Everyone hosts trillions of bacteria in their gut and millions more in places like their skin and mouth.
This collective microbiome has been linked to nearly every aspect of physical and mental health, from digestion to depression.
The Microbiome Master Key reviews the research to show how supporting the microbial ecosystems in our bodies and environments may be a powerful way to live and age well.

“Am I human, or am I bacteria?”

The question sounds like something out of Star Trek, but it popped into my head around chapter four of The Microbiome Master Key, and I couldn’t shake it. Written by Brett Finlay and Jessica Finlay — yes, they’re a related father–daughter scientist duo — the book explores how the microbes living in and on us shape nearly every aspect of human health.

“Microbes,” short for microorganisms, are tiny living things like bacteria, viruses, fungi, and protozoa. When scientists talk about the human microbiome, they usually refer to the trillions of bacteria that live in and on our bodies, especially in the gut.

Like many people, I had a vague sense that gut bacteria help with digestion. I eat yogurt and drink the occasional kombucha partly because I assume it’s “good for my gut.” I even knew the classic fun fact: By sheer number of cells and DNA, we’re more microbial than human.

However, the Finlays’ book challenged my assumption that my microbiome was made up of mostly passive passengers. Instead, the authors show that it is essential to almost every part of how we function: healing, sleeping, how our skin looks, and maybe even how we think. The connection made me reconsider, well … what actually “am” I?

In an interview, I asked Brett if studying the microbiome made him question things like free will, agency, or identity. He chuckled the way a scholar does when someone new to their field finally has that “Aha!” moment.

“Learning more about your microbiome will certainly shake your definition of what it means to be human,” he says.

A microbiologist and professor at the University of British Columbia, Brett has spent decades immersed in the world of bacteria. In his classes, he tells students to look around the room and describe what they see. “Where they say ‘human,’ I say, ‘Yes, a human, but also a vessel for bacteria.’”

Jessica, a geographer, environmental gerontologist, and assistant professor at the 91PORN, brought a more relational view. She described microbes as her “lifelong invisible partners.” “We give them a home and food,” she said. “In return, they help us function. They’re with us from birth to death. You don’t really get to opt out.”

While that thought might elicit cringes from some readers, the reality is far from a germophobic nightmare. That’s because embracing your microbiome may be, as the authors put it, the real “master key” to better health and aging.

Rewriting the microbial story

This perspective motivated the Finlays to update their 2019 book, The Whole Body Microbiome, and expand it with new chapters and fresh research in The Microbiome Master Key.

“Really, this is the book we wanted to write five years ago,” Brett tells me. “Back then, we had hints that microbes weren’t just important in the gut but critical to many functions. The research wasn’t strong enough to make a compelling case, though.”

Today, it is, and the Finlays have pulled together the evidence linking the microbiome to a wide-ranging — and, frankly, almost unbelievable — list of health outcomes: from chronic inflammation to cognitive decline, from depression to physical fitness, from better sleep to more youthful skin.

Beyond sharing the new research, the Finlays were also motivated to update the book because they felt we may be on the edge of a mindset shift — one that could influence whether we, collectively, choose to embrace our microbes.

“We’ve spent the last 120 years trying to kill bacteria so we don’t die from infectious diseases,” Brett explains. Over time and alongside revolutions in medicine, hygiene, and sanitation, germs became public enemy number one. But more recently, people have started to embrace the idea of the gut microbiome.

“We were moving in a good direction when the public was embracing the importance of the gut microbiome,” Jessica adds. “People were encouraging kids to play in the dirt, backing off hand sanitizer a bit, eating fermented foods to support their microbiome. Then COVID hit, and understandably, people became terrified of germs again.”

The Finlays aren’t against fighting infectious diseases or practicing good hygiene, of course. They simply argue that our post-pandemic recoil into extreme cleanliness risks disrupting the delicate microbial ecosystems our bodies depend on to thrive.

Gut check: The microbiome’s central hub

The human gut is home to an astonishingly diverse and abundant community of microbes, estimated at over 100 trillion bacteria. That’s roughly equivalent to the number of human cells in the body. Among these are hundreds of unique species, many of which live in the colon and large intestine.

We pick up most of our gut bacteria early on, starting with a major dose during the journey through the birth canal. From there, the microbiome tends to stabilize through adulthood as we’re exposed to microbes in our environment and from the people around us. Interestingly, it begins to shift again as we age. People over 65 often show a different balance of key bacterial groups and tend to have more microbes associated with inflammation.

“When you study the microbiomes of people with many of the world’s most pressing conditions, you’ll find a microbial signature associated with them,” said Brett.

In other words, many conditions — such as obesity, cancer, liver disease, heart disease, and neurodegenerative disorders — are associated with a shift in the microbiome. Certain microbial species may be present or missing; imbalances in microbial function may have occurred. Researchers are still working to determine whether these patterns play a role in causing disease or are associated with it. Still, one thing is clear: The pattern emerges again and again across a wide range of diseases and conditions.

Early in my reading, I wondered: What causes the microbiome to shift away from a community that supports health? A major culprit is diet.

Ultra-processed foods — anything from Pop-Tarts to protein powder — are called “ultra-processed” for a reason. They’re so refined that your body can break them down and absorb them early in the digestive tract, so they never reach the large intestine where many beneficial microbes live. As a result, those microbes are essentially starved of the complex fibers they rely on to survive and thrive. In Western countries like the United States, ultra-processed foods now make up a growing portion of the typical diet.

Antibiotics are another disruptor unique to modern life. While lifesaving in many cases, antibiotics don’t discriminate: They wipe out harmful pathogens and beneficial gut bacteria alike. In the book, the Finlays note studies that detected changes to the microbiome up to four years after a single course of treatment.

Then there’s the obsession with cleanliness. Our environments are increasingly sanitized, and while that helps prevent infections, it also limits our exposure to the diverse microbes our guts evolved alongside.

Add up these habits and stressors, and over time, your gut begins to support a different kind of microbiome, one that may include harmful species. And, as the Finlays argue, a changing microbiome can have systemic effects on physical and mental health.

The microbiome and the immune system

One of the key ideas in The Microbiome Master Key is that your gut microbiome plays a powerful — though still not fully understood — role in regulating your immune system.

Several patterns suggest a strong link between the gut and the immune response. For one, the gut houses 70–80% of the body’s immune cells. In addition, low-grade inflammation tends to increase as we age. At the same time, the composition of the gut microbiome shifts, often to favor microbial species associated with inflammation.

Taken together, these observations suggest a possible connection between age-related inflammation and changes in the gut microbiome.

Researchers are beginning to uncover mechanisms that support this idea. Certain gut microbes produce signaling molecules that help train immune cells to distinguish between harmless and harmful substances. Since the immune system constantly samples its environment through the gut, a well-balanced microbiome may help prevent overreactions (like allergies and autoimmune disorders) and under reactions (which can leave the body vulnerable to infection).

The emerging evidence also shows that disruptions in the gut microbiome can contribute to autoimmune conditions outside the gut. For instance, people with rheumatoid arthritis or multiple sclerosis often have altered gut microbial communities. These findings suggest that supporting a balanced microbiome could be one way to reduce low-grade inflammation and potentially help prevent or manage age-related and autoimmune diseases.

The mind-gut connection

We tend to think of the brain as the body’s command center, but more and more, it looks like the gut microbiome has a prominent say in the conversation. For me, the idea that bacteria in your gut could affect your mood, anxiety levels, and even cognitive function was one of the book’s biggest “Wait! What?” moments.

Brett wasn’t surprised by my fascination. “The potential of the gut–brain axis is the most exciting area of research for most people,” he tells me. He’s referring to the complex communication network between the gut and the brain, which includes a major nerve called the vagus nerve.

This nerve isn’t a one-way street. The brain regulates gut function, but the gut sends signals back, and that’s where microbes come in. Research suggests the microbiome may influence the brain by producing neurotransmitters or interacting with gut neurons connected to the vagus nerve.

There is also growing evidence to link disruptions in the gut microbiome to various conditions, such as stress, depression, and anxiety. For example, the Finlays highlight one study where researchers transferred fecal matter from stressed rodents into healthy ones. Afterward, the healthy animals began showing signs of stress themselves. The researchers changed the animals’ moods and behaviors simply by changing their gut microbiota.

Another study found that people who had taken just a single course of antibiotics in the past year had a significantly higher risk of developing depression. There’s also emerging evidence connecting the microbiome to neurological conditions like Parkinson’s, Alzheimer’s, and even stroke. (It was around this time in the book that I had my “who am I?” moment).

Although a complete picture of the gut-brain relationship is still evolving, the knowledge is already actionable. The Finlays reference the MIND diet (short for Mediterranean-DASH Intervention for Neurodegenerative Delay), a plant-forward dietary approach that includes leafy greens, berries, poultry, and fish to reduce the risk of cognitive decline.

“People who follow this diet have delayed the onset of Parkinson’s by up to 17 years,” Brett points out. The book also cites studies showing that the MIND diet can reduce the risk of Alzheimer’s by as much as 50%.

Turns out, this brain-friendly diet is exactly what people’s gut microbes thrive on. So, while scientists are still working out the details, the overlapping evidence suggests one promising explanation: It may support brain health, at least in part, by supporting the microbes in your gut.

Beyond the gut and beyond the body

Microbes aren’t just in the gut. On the skin, they help create chemicals that maintain our protective barrier, may influence whether you sunburn, and even hold the key to pesky signs of aging like wrinkles. In the mouth, they affect gum health and possibly heart health.

It doesn’t stop at the surface, either. As Jessica points out, your microbes aren’t just in you. They’re all round you.

“Your zip code is one of the biggest predictors of how long you live,” she notes, and after immersing herself in microbiome research, she’s come to believe that microbes may help explain why place matters so much.

When you touch your counter? Microbes. A door handle? Microbes. Package from Amazon? More microbes. A handshake or hug? Think of it as a microbial swap. For some, the idea that microbes are everywhere might sound alarming, but the Finlays argue that this constant exposure isn’t something to fear. It’s something to design for.

“There’s a huge opportunity in public policy and architecture,” Brett says. “We can build environments that support microbial health, not just sterilize it away.”

Jessica adds, “Imagine hospitals, schools, and care homes designed not only to keep pathogens out, but to support beneficial microbes.”

In that case, how do we take care of our microbiome and ensure it’s populated with good stuff?

The advice will sound familiar: Eat a primarily plant-based diet (microbes love fiber), exercise regularly (physical activity seems to support a more diverse and resilient microbiome), stay socially connected, reduce stress, and get enough sleep. Less common but still beneficial advice includes enjoying more fermented foods, opening the windows in your home to let the air in, and getting outside in nature.

As for probiotics, the Finlays note, they likely won’t hurt, but there’s little evidence they do much to broadly support the microbiome.

Unsurprisingly, something as fundamental as our microbial ecosystem thrives when we follow the same habits we already know support human health. But that raises another question: What does the microbiome lens add if the lifestyle advice remains the same?

“Understanding why these activities could benefit my microbiome, and by extension, me, gives me a more fundamental, ecological understanding of why these actions help,” Jessica says. “And that type of knowledge is more motivating and meaningful.”

She adds, “I love that I don’t have to recommend some crazy supplement or strict regimen. It’s just eating well. Open a window. Go outside. Shake hands. Move your body. Knowing that all these things help my microbiome just makes me want to do them more.”

As someone who tries, but admittedly doesn’t always succeed, in following that advice, I asked them what they’d recommend to an overworked person who is stressed out, potentially sick, and fresh off a regimen of antibiotics.

“The best thing about the microbiome is that you can change it,” Brett says. “You can’t change your human DNA. But bacterial DNA? That’s flexible.”

He told me that even in animal studies where the microbiome has been nearly wiped out, introducing basic conditions like healthy food can restore balance within days.

“They’re all around us,” he says. “If you take antibiotics, for example, and start taking simple, proactive steps — like eating fermented foods, spending time outside, or adjusting your habits to support them — they’ll find you. And once they do? Those beneficial functions kick in fast.”

The future of microbiome science

Despite all the exciting ways microbiome intersects with human health, Brett and Jessica don’t ignore some of the big knowledge gaps in the field. Ironically, we still don’t have a clear definition of what a “healthy” microbiome even is. There’s no universal set of microbial species that defines good health. Different people can have diverse microbiomes and still be perfectly healthy.

“If the microbiome is so fundamentally important, why don’t we all have similar microbial communities?” Brett asked. “It’s a central question and a sticking point in microbiome research.”

The leading theory, he explains, is functional redundancy — the idea that different microbes can perform the same roles. “Even though the bacterial makeup might differ, the functions they carry out are relatively conserved across people.”

You can tell that applied use, clinically and in public policy, is where the Finlays believe and hope the science is heading. Throughout the book, they sketch out futuristic possibilities that may be closer than you think: preventing diseases with the microbiome, personalized supplements tailored to your unique microbiome, bacteria-informed skincare, microbial interventions to boost athletic performance, the list goes on.

I think … therefore I host?

The Microbiome Master Key is a technical and scientific book at heart, but the Finlays also strike a surprisingly personal tone. In fact, the book reads like an ode to the underappreciated microbes that make us who we are.

By the end of our conversation, I wasn’t as concerned with whether I had “true agency” or if bacteria were secretly calling the shots. In the end, it’s all still me.

Maybe Descartes had it wrong. Maybe I think … because we are?

In “The Microbiome Master Key,” Brett and Jessica Finlay argue that we need to stop waging war on all germs and start working with the microbes that make us who we are.

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Jessica Finlay Receives Emerging Scholar Award in Health and Medical Geography

Anonymous — Wed, 01 May 2024 14:18:23 +0000

Jessica Finlay Receives Emerging Scholar Award in Health and Medical Geography Anonymous (not verified) Wed, 05/01/2024 - 08:18

During the 2024 Association of American Geographers (AAG) meeting in Honolulu, Hawaii, Dr. Jessica Finlay was awarded the Emerging Scholar Award in Health and Medical Geography. This is a highly competitive award. According to the AAG website, this award "seeks to recognize early career scholars who show significant potential for distinguished scholarship in health and/or medical geography." Dr. Finlay will be invited to give a special symposium talk on her research during the 2025 AAG conference in Detroit, Michigan.

We look forward to her symposium talk!

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Jessica Finlay presents to the National Academies

Anonymous — Tue, 19 Dec 2023 20:51:47 +0000

Jessica Finlay presents to the National Academies Anonymous (not verified) Tue, 12/19/2023 - 13:51

New Assistant Professor, Dr. Jessica Finlay was part of an "Aging in Place with Dementia" workshop hosted by the National Academies of Sciences, Engineering, and Medicine. She presented her Cognability research to investigate how neighborhood built and social environments impact brain-healthy activities and risk for Alzheimer's disease in later life. You can learn more about the workshop here and check out your neighborhood's Cognability score here.

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Jessica Finlay joins the Department of Geography and Institute of Behavioral Science

Anonymous — Tue, 19 Dec 2023 20:47:02 +0000

Jessica Finlay joins the Department of Geography and Institute of Behavioral Science Anonymous (not verified) Tue, 12/19/2023 - 13:47

Jessica is a health geographer who uses mixed methods to investigate how built, social, and natural environments impact health and wellbeing across the life course. She has developed a new concept, Cognability, to capture how neighborhoods may support brain health through opportunities to exercise, socialize, and think/learn in later life. You can check out a preliminary Cognability score for your neighborhood here.

Jessica grew up on the other side of the Rocky Mountains in Vancouver (Canada). When not at her desk, Jessica is most often chasing after her two fast-moving children (aged 2 and 4), running the 91PORN trails with her partner Matt, or curled up with a pop fiction book.

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