There was a moment during the Lewis and Clark expedition of 1804 when, after months of deprivation, hardship, and arduous climbing, they finally scaled the eastern face of the Continental Divide. Standing exhausted on that peak, they hoped to gaze down on gentle meadows and the gateway to the sea, but instead they saw…more mountains. It was mountains as far as the eye could see.
In some ways, modern biology has followed the same trajectory: in the 70's we believed we were within striking distance of the cure for cancer, steps away from enlightenment about our own internal processes. Now we know it's a much bigger expedition than we ever anticipated.
When it comes to understanding the body, the complexity we face is mind-boggling, a thick and tangled web of feedback loops and inner dependencies. Take, for example, the human gut.
For years, it's been relegated to the back bench of physiological study. Recently, we've begun to see that the digestive tract is, in fact, a star in its own right. Those less glamorous organs are rising to costar status with the brain. The two are sometimes described as a team: the brain/gut axis. According to Giulia Enders in her new book, Gut: The Inside Story of Our Body’s Most Underrated Organ, there is incredible crosstalk between the two.
The human brain contains about 86 billion neurons. The gut, meanwhile, contains only 100 million neurons—on par with the brain of a cat. So, in the neuron department, the brain generally calls the shots. But the gut calls more than a few plays of its own.
Your gut houses a teeming microbiome of bacteria that affects your daily life in myriad ways. What goes on in your gut shapes your immune system, nutrition absorption, vitamin production, muscle function, hormone levels, libido, whether you're hungry or full, and how you break down your food intake into proteins, carbohydrates, and fats. Your gut’s microbiome weighs in at about 4.5 pounds and Enders says some scientists are beginning to refer to it as a separate body organ.
Gut-related chronic health problems include allergies, cancer, Type II diabetes, mood swings, and anxiety. The bottom line: your gut is far more auxiliary brain than mere food dumpster.
Your vagus nerve, the longest of the twelve cranial nerves, is the superhighway connecting the brain to the gut. The gut also produces 95% of the neurotransmitter serotonin. Sometimes called the "feel-good" hormone, serotonin is strongly linked to your levels of happiness and depression. Your gut also makes GABA, an amino acid that calms the nervous system and smooths out brain waves, and a neurotransmitter called glutamate, involved in cognition, learning, and memory.
Your food choices have a direct effect on your gut's microbiome. For that reason, Enders says it's probably a good idea to eat a diet rich in probiotics (although more research is needed to confirm healthful benefits.) These are bacteria and yeast that support digestive health, found in fermented foods like kim chi, sauerkraut, kefir, pickles, and plain unsweetened yogurt.
According to Enders, these foods may help maintain the integrity of the gut lining, and that they serve as natural antibiotics, antivirals, and antifungals. They also play a role in regulating your body's immune system. This in turn helps control inflammation and improve nutrient absorption.
There are many more summits to climb before we have a clear map of what goes on inside the belly's hidden kingdom, but like Lewis and Clark, the discoveries we make continue to amaze. And yet for all our newfound knowledge, we've only begun to gain a tenuous foothold—and there are still mountains as far as the eye can see.