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The Garden in Your Gut

By Amanda Kolson Hurley

Probiotics and fermented foods are all the rage for digestive health, but do they really work? Here’s what scientists are discovering about the trillions of microbes that live in our bodies and how this complex ecosystem—which some call the “second brain”—influences not just our digestion but our overall well-being.

In the first scene of his tragedy Coriolanus, Shakespeare weaves a vivid metaphor of the Roman republic as a human body, an organism that can’t function unless all its constituent parts work together. The Roman Senate rules this body, but not as its head—as its belly.

 

The belly, explains a senator in the play to a rebellious commoner, delivers its sustenance to all your limbs and organs, “through the rivers of your blood, / Even to the court, the heart, to the seat o’ the brain.” In the same manner, he says, the Senate “digest[s] things rightly / Touching the weal o’ the common,” then disburses its largesse (as grain rations) to the common people. The moral is that every person in the republic, each lowly finger and toe, owes its well-being to the belly of the Senate. Shakespeare adopted this story from Aesop, who had a fable of “the belly and its members.” 

 

To modern eyes, the notion that our bellies could rule us seems quaint. We know the incredible power of our brains, thanks to neuroscience. We know that our hearts pump nutrient-rich blood around our bodies. But Shakespeare and Aesop were onto something. Researchers now believe that our digestive systems (or guts, to use the blunt Shakespearean word) play an important and far-reaching role in our health that is still not fully understood. The digestive tract, from the esophagus to the stomach and intestines and down to the rectum, functions less like a simple machine and more like a complex ecosystem. Many scientists have even taken to calling the gut and its microbiome “the second brain” and the legion of microbes that live there “the hidden organ.” 

 

The human gut is home to a microbial population of staggering diversity. Each of us has 100 trillion microbes in our body at any given time, most of them in our lower intestines. Together, they weigh two pounds or more. The microbial genes in our bodies outnumber our human DNA by a factor of 100 to 1. 

 

Our gut microbiota—the unique mix of bacteria, viruses, protozoa, and other bugs inside our intestines—influences our weight and likelihood of developing gastrointestinal disorders, like irritable bowel syndrome and inflammatory bowel disease, as well as type 2 diabetes. It could also be a factor in conditions including rheumatoid arthritis, depression, and autism, though research on such connections is still in its infancy. 

 

Gerard Mullin, an associate professor of medicine at Johns Hopkins University and the director of Integrative GI Nutrition Services at Johns Hopkins Hospital, describes the gut flora as a garden, a “magnificent orchard” of single-cell life. “When I was in medical school, we were told that [gut microbes] were kind of vestigial—they were just there,” he recalls. “I think we’re just starting to understand that they’re vital, and the better their health is, the better our health is.” 

 

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Around 1,000 different species of bugs live in your gut. We acquire them at birth (initially in the birth canal) and during the early years of childhood. What do they do, exactly?