‘A healthy gut can equate to a healthy body’ — how physicians can explain the gut microbiome

The notion of using the gut as the starting point to treat illness goes back at least to the time of Hippocrates.

But then, everything old becomes new again, and physicians and patients have been inundated with claims about the good, the bad and the upsetting in the human digestive system.

The good is that contemporary research is leading to discoveries that affirm the importance of gut health at all stages of life. The findings are encouraging and there’s more to learn. Yet claims about cure-alls may be a waste of time, money and resources. Some products and practices could hurt gut health, not help it. GLP-1 drugs that affect digestion and the gut-brain axis continue to be one of the hottest topics across medicine.

Financially, gastrointestinal (GI) diagnoses and treatments are no small part of U.S. health care. GI-related expenditures hit $111.8 billion as of 2021.

The “Mayo Clinic Guide to Gut Health: Restore your microbiome, enhance digestion, and improve your health from the inside out,” by gastroenterologist and hepatologist Sahil Khanna, M.B.B.S., M.S., is a patient-facing volume with the latest information about the stomach, intestines, liver and pancreas.

This excerpt is taken from chapter 3, “The microbiome universe,” and makes a starting point for discussion when patients ask: What exactly is the gut microbiome?

The book is available through Mayo Clinic Press. For the latest clinical roundup on the science of gut health, Khanna also is a co-author of the “International consensus statement on microbiome testing in clinical practice,” published in February in The Lancet Gastroenterology & Hepatology.

The microbiome universe

The human gut is a living ecosystem. Similar to the diverse plant species seen in a rainforest, trillions of bacteria, fungi, viruses and other microorganisms reside within the gut, forming a complex ecological universe called the gut microbiome. For centuries the microbiome was viewed mainly as a tool to aid in digestion. Not any longer.

More than two decades of microbiome research has provided mounting evidence that the microorganisms that live inside of us, especially those in the gut, have a profound effect on not just our digestive health but also our overall health and well-being. Changes to a person’s microbiome — alterations in the diversity of organisms that call your gut home — are associated with a range of diseases from cancer to obesity and everything in between.

It’s for this reason that your gut and how to care for it have taken on a whole new light. A healthy gut can equate to a healthy body.

There’s much still to learn, and many questions about the gut microbiome still linger. As you read through this chapter, keep in mind that for most of the condi- tions discussed, there’s only an association between the condition and an unhealthy gut microbiome. Gut imbalances haven’t yet been proven to be the cause. It’s also not always clear what comes first: Does a gut imbalance trigger disease, or does a disease lead to an unbalanced microbiome?

THE MICROBIOME EXPLAINED

In various parts of our bodies — in the mouth, vagina or respiratory tract, for example — we host a wide variety of microorganisms. But nowhere are these microorganisms greater in number and diversity than in the gut. Diversity refers to the number of different species of microorganisms in the gut and how evenly distributed they are. Diversity is crucial, as it’s a hallmark of a healthy gut.

Most of the time the right kind and the right amounts of microorganisms are taking up residence in our guts, communicating with almost every area of our body and helping us maintain good overall health. But sometimes the balance of these microorganisms can be disrupted, causing a reduction in good bacteria, for example, and an increase in potentially harmful bacteria. Research is continuing to explore how such imbalances may be related to disease, from conditions that probably aren’t so surprising, such as digestive disorders, to those you may not expect, such as autism.

One of the largest undertakings has been the National Institutes of Health’s Human Microbiome Project. Launched in 2007, it helped catalog bacteria present in humans at various sites in the body, with the goal of learning what a healthy human gut is and whether human health could be improved by changing the gut’s microbial makeup.

Early beginnings

The formation of the gut’s microbial ecosystem begins in infancy. Research suggests that before birth, our digestive tracts are like a blank slate. With birth, many outside influences begin to help shape the makeup of our guts. For example, an infant born via a vaginal delivery will have gut bacteria that differ from those in an infant born via a cesarean section. This is because the mother passes along bacteria to her child during a vaginal delivery. Babies who are breastfed will have a different gut makeup than babies who consume formula. By the time a child is a toddler, the child’s gut microbiota starts becoming more diverse. All old, our bodies house about 100 trillion gut microorganisms, including several hundred different species of bacteria.

These microorganisms provide many benefits, including strengthening the digestive tract, providing nutrients such as vitamins, regulating metabolism and protecting you from invaders that can cause disease. Gut microorganisms also play a role in communication with your immune system and regulating immunity.

What’s a healthy microbiome?

A simple definition of a healthy gut microbiome is a gut microbiome where microbiota maintain a stable, mutually beneficial relationship. The wide variety of microorganisms is balanced, with no overgrowth of harmful bacteria that could interfere with gut functions. A healthy microbiome features microbes working together to help with activities such as digestion, production of useful substances such as vitamins and short-chain fatty acids, and protection against harmful microbial invaders. A healthy gut also can operate normally despite dietary changes, stress or other outside influences.

Certain factors, however, can alter the mix of microbes and how they function. One example is medications. Another is a change in diet. Aging also can have an impact because the microbiota in our guts tend to become less diverse as we get older.

Decreased microbial diversity can result in overgrowth of harmful bacteria leading to conditions such as Clostridioides difficile (C. difficile) infection. An imbalance may also be linked to other gastrointestinal conditions, such as irritable bowel syndrome (IBS) and inflammatory bowel disease (IBD), to illnesses such as allergies and obesity, and to neurological issues, such as autism and Alzheimer’s disease.

GUT DISRUPTORS

The term dysbiosis refers to an imbalance in the gut microbiota, where there’s an excess of harmful bacteria, a lack of beneficial bacteria or a general loss of diversity within the microbial community. Dysbiosis can interfere with the functioning of beneficial gut microbiota in charge of maintaining your health.

Several factors can lead to an imbalanced, or unhealthy, gut. They include diet, medications, smoking, stress and environmental pollutants.