When most people think about the human body, they imagine that we're made up almost entirely of human cells. It seems logical, right? Surprisingly, that's not the whole story.
Each of us carries roughly 30 trillion human cells and about 39 trillion microbial cells—primarily bacteria—living in and on our bodies. Most of these bacteria reside in the large intestine, also known as the colon. Think about that for a moment. You are home to an entire ecosystem that is just as much a part of you as your heart, lungs, or brain.
For many years, scientists believed bacteria were something to avoid. While it's true that certain bacteria can cause illness, we now know that the vast majority of the bacteria living inside us are actually beneficial and essential for good health.
In many ways, we're not just human. We're human plus trillions of microscopic partners working around the clock to keep us healthy.
Why Do We Have So Many Bacteria?
The relationship between humans and bacteria began millions of years ago through evolution. As humans evolved, so did the microorganisms living alongside us. Over time, we developed a mutually beneficial relationship known as symbiosis.
In simple terms:
We provide bacteria with a warm, safe place to live and a constant food supply.
In return, they perform countless jobs our bodies either can't do efficiently—or can't do at all.
It's one of nature's most remarkable partnerships.
What Do Gut Bacteria Actually Do?
Your gut bacteria are incredibly busy every single day.
They help:
Digest foods that your body cannot break down on its own.
Produce important vitamins such as vitamin K and several B vitamins.
Create short-chain fatty acids that nourish the cells lining your colon.
Support your immune system and help train it to recognize harmful invaders.
Protect against harmful bacteria by competing for space and nutrients.
Strengthen the intestinal barrier, helping prevent unwanted substances from entering the bloodstream.
Communicate with your brain through what scientists call the gut-brain axis, influencing mood, stress, memory, and cognitive function.
Help regulate metabolism, blood sugar, inflammation, and even body weight.
In other words, these tiny organisms are quietly working behind the scenes every moment of the day.
Your Gut Is Like a Garden
One of my favorite ways to explain the microbiome is to imagine your gut as a garden. Every meal either feeds the flowers or feeds the weeds. When you regularly eat whole, plant-based foods—vegetables, fruits, beans, lentils, whole grains, nuts, seeds, herbs, and spices—you provide fiber that your beneficial bacteria absolutely love. As these bacteria ferment fiber, they produce compounds that help reduce inflammation, strengthen your immune system, protect the lining of your gut, and support overall health.
On the other hand, diets high in ultra-processed foods, refined sugar, excessive alcohol, and low in fiber can reduce bacterial diversity and allow less beneficial bacteria to flourish. Over time, this imbalance—called dysbiosis—has been associated with digestive disorders, obesity, type 2 diabetes, inflammatory bowel disease, allergies, autoimmune conditions, and even changes in mood and mental health.
Diversity Matters
One of the biggest discoveries in microbiome research is that a diverse microbiome is generally a healthier microbiome. Different bacteria specialize in different jobs. Some produce anti-inflammatory compounds. Others digest certain fibers. Others help regulate the immune system. The more diverse your gut community is, the more resilient it becomes.
One of the simplest ways to encourage diversity is by eating a wide variety of plant foods. Researchers have found that people who consume 30 or more different plant foods each week tend to have greater microbial diversity than those who eat fewer varieties.
That doesn't mean 30 servings—it means 30 different foods.
For example:
Spinach
Kale
Broccoli
Blueberries
Apples
Black beans
Lentils
Quinoa
Walnuts
Flaxseed
Each plant feeds different groups of beneficial bacteria.
We Are Not Just Feeding Ourselves
This is one of the concepts I love sharing with clients. When you sit down to eat, you're not only feeding your body—you are feeding trillions of living organisms that help determine how your body functions. Every meal is an opportunity to build a healthier internal community. It's a perspective that changes how we think about nutrition.
Instead of asking, "How many calories are in this?"
We might ask,
"What am I feeding my microbiome today?"
Final Thoughts
The human body is truly remarkable. It has evolved alongside trillions of bacteria that quietly support nearly every aspect of our health—from digestion and immunity to brain function and inflammation. The more we learn about the microbiome, the more we realize that health isn't just about taking care of ourselves. It's also about taking care of the tiny ecosystem living within us.
Every colorful vegetable, every serving of beans, every piece of fruit, every handful of nuts and seeds is an investment in that community. And when that community thrives, we often do too.
Sometimes the smallest living things can have the biggest impact on our health.
To Health & Longevity, 🌿
Innovative Wellness
References
Sender, R., Fuchs, S., & Milo, R. (2016). Revised Estimates for the Number of Human and Bacteria Cells in the Body. PLOS Biology, 14(8), e1002533.
Gilbert, J. A., Blaser, M. J., Caporaso, J. G., Jansson, J. K., Lynch, S. V., & Knight, R. (2018). Current understanding of the human microbiome. Nature Medicine, 24, 392-400.
The Human Microbiome Project Consortium. (2012). Structure, function and diversity of the healthy human microbiome. Nature, 486, 207-214.
Sonnenburg, J. L., & Sonnenburg, E. D. (2019). The Good Gut: Taking Control of Your Weight, Your Mood, and Your Long-term Health.
American Gastroenterological Association. Understanding the Gut Microbiome.