The human gut is a vast ecosystem of microbes, far older than modern humans, that play a critical role in processing food and influencing health. Modern diets, often lacking fiber and rich in processed foods, are drastically altering this microbial diversity, with researchers exploring the profound two-way relationship between diet, microbiome, and human biology.

The human gut is a vast ecosystem of microbes, far older than modern humans, that play a critical role in processing food and influencing health. Modern diets, often lacking fiber and rich in processed foods, are drastically altering this microbial diversity, with researchers exploring the profound two-way relationship between diet, microbiome, and human biology.

The human gut is a vast ecosystem of microbes, far older than modern humans, that play a critical role in processing food and influencing health. Modern diets, often lacking fiber and rich in processed foods, are drastically altering this microbial diversity, with researchers exploring the profound two-way relationship between diet, microbiome, and human biology.

We like to think of ourselves as the dominant species on Earth. But from a microbial point of view, we are newcomers. Bacteria and archaea have been around for more than 3.5 billion years. Modern humans have existed for only around 200,000 years. And microbes are everywhere, in soil, water, plants, animals, and most importantly, inside us. One of the most remarkable microbial communities lives in our gut.

Your gut is an ecosystem

Think of your digestive system as a long tube running from your mouth to your anus. Different sections of this tube create very different environments for microbes.

The stomach, with its highly acidic environment, has relatively few microbes. Their numbers increase further down the digestive tract, with the largest microbial community living in the colon.

Your colon is home to trillions of bacteria. Many of these bacteria feed on dietary fiber that our own digestive enzymes cannot fully break down. In return, they produce compounds that can influence processes such as metabolism and immune function.

So when you eat fibre, you are not only feeding yourself. You are feeding your microbial community too.

What happens when our diet changes?

For most of human history, diets contained plenty of plants, fibre and minimally processed foods. Modern diets, particularly in industrialised societies, often contain considerably more ultra-processed foods and less fibre.

Researchers studying traditional populations, including the Hadza of Tanzania, have found striking differences in their gut microbiomes compared with people living more industrialised lifestyles. Their diets are typically much higher in fibre, and their gut microbiomes tend to contain greater microbial diversity.

This doesn't mean that a particular traditional population has the 'perfect' microbiome. But it raises an important question: what happens to our microbial ecosystem when our environment and diet change dramatically within just a few generations?

Scientists are increasingly interested in this because a diverse microbial ecosystem may be more resilient; rather like a forest containing many different species may be better equipped to adapt to change.

What do these microbes actually do?

Your gut bacteria aren't just sitting there. They are constantly interacting with what you eat and with your body.

When certain gut bacteria break down fibre, they produce compounds that can affect the cells lining your gut, interact with the immune system and influence aspects of metabolism. In that sense, your gut microbes are active participants in your biology.

Scientists have even found that changing the microbiome can change metabolism in animals. In one well-known experiment, researchers transferred gut microbes from mice with obesity into germ-free mice. The recipient mice subsequently gained more body fat.

That doesn't mean we can simply blame our weight or health on our gut bacteria. Human biology is far more complicated, and the microbiome is only one piece of the puzzle. Researchers have found associations between changes in the gut microbiome and conditions such as inflammatory bowel disease and metabolic disorders, but association does not necessarily mean causation.

What we do know is that the relationship works both ways: our diet and lifestyle shape our microbial community, and our microbial community can influence how our body responds to what we eat.

We are only beginning to understand the ecosystem

Modern DNA-sequencing technology has transformed how we study the microbiome. Instead of looking only for individual bacteria that cause disease, scientists can now study entire microbial communities.

And that has changed the question.

We are no longer asking only, "Which bacteria are harmful?"

We are beginning to ask, "Which microbes live with us, what are they doing, and how does the way we live affect them?"

Perhaps the most useful way to think about your gut is not as a sterile machine that occasionally gets invaded by bacteria, but as an ecosystem that is already teeming with life.

The opinions expressed in this article are those of the author and do not purport to reflect the opinions or views of THE WEEK.

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