The second brain in our gut and why its well-being is critical

I suffered from poor digestion for about five years and aside from the pain, I had days where I was anxious about leaving known territory for fear of a lack of toilets. I did a lot of research trying to solve my problems and concluded that eliminating trigger foods was the best course of action. I cut out dairy first. That did help, for a while. But then in a couple of weeks the cramps came back. The pattern of improvement and regression repeated as I eliminated other foods my diet, including tea, Coca Cola, sugar, wheat, and even potato chips. At which point my friend Beatrice asked me, “Why live?” But with my limited diet I was at least able to venture forth and had started to accept my lot. Then my nurse practitioner suggested I try a probiotic - Culterelle’s Women’s Health Balance. I’m not much of a believer in supplements, and I probably sneered when she said it. But … I figured I didn’t have anything to loose. After a couple days of taking the probiotic, I was like a new human. My gut felt better and my energy levels rebounded. Then the penny dropped: my gut problems had all started around the time I’d taken antibiotics to clear up a kidney infection. If I’d known then what I know now, I could have had 5 more years of ice cream sundaes. Such a loss.

Let’s start with the basics. The human gastro-intestinal (GI) tract includes the mouth, the esophagus, the stomach, the intestines, and the rectum. Food travels down this system of tubes assisted by muscles, that reside in a layer within the tubes’ walls. This layer of muscle contracts forcing the food to flow in the right direction. As the food travels down the tract it is broken down mechanically and chemically into smaller and smaller chunks until it is either absorbed into the body or expelled. One of the wonders of our bodies is that while we want to absorb the nutrients and energy packets of the broken down food, we don’t want the dangerous bacteria and pathogens in the food to enter our bodies. So we’ve developed a few layers of protection. A big part of this defense is the inner most layer of the tubes in our GI tract, called the mucosa. The mucosa comes into direct contact with food and is responsible for most digestive, absorptive and secretory processes, and keeps pathogens from entering the human body. It’s an effective gate keeper. Another part of keeping unhealthy microorganisms out of our bodies is our immune system. In fact, 70% of our immune system is targeted on the GI tract.

Between the muscular -push the food along-layer and the mucosal -digest and protect -layer there is a third layer - rather uncreatively called the submucosa layer. Fascinatingly, the submucosa layer contains a network of 100 million neurons and is called the enteric nervous system. There are more cells in this neural network than in the parasympathetic and the sympathetic nervous systems combined. Neurons are electrically excitable cells that can communicate with other cells via synapses and the ones in our gut work like the neurons in the rest of our body. But unlike other systems within our body, the guts neural network acts mostly independently from the head’s brain. Instead it’s the other way around, the enteric nervous system tells the brain what to do. A full 90% of the signals sent between the gut and the brain, along the so-called vagus nerve, flow from the gut to the brain. Scientists are know recognizing that the idiom “gut feeling” may well be an accurate description of where the feelings come from. Our enteric nervous system may well be nudging us towards a given decision. Other feelings like “butterflies in your stomach”, “gut wrenching”, and “pit in my stomach” may also be from our enteric nervous system and have helped to earn the enteric nervous system the nickname “The Second Brain”. Some researchers have even posited the enteric nervous systems was in fact our first, more primitive, brain.

But the wonder of digestion doesn’t stop there. Within the tubes of the human GI tract is an entire ecosystem of non-human micro-organisms. Billions of them. In fact, 10,000 billion, or 100,000,000,000,000, non-human micro-organisms live in your gut. This is about as many human cells as are present in our bodies and about 1,000 times more than the number of stars in the milky way. Each of us has about 2000 species of non-human creatures living in our gut and together they have over 100 times as many genes as we do. Bizarre. It’s not just humans who have ecosystems within them, all animals and plants form mutually beneficial associations with microorganisms, like the microrhizal fungus network that plants rely on.

We are just beginning to understand the many roles of our microbiota. Here are some of the things we know those little guys get up to. Our microbiome aids digestion and the extraction of energy and nutrients from our food, keeps our immune system functioning properly, and synthesizes essential vitamins like B and K. Our gut’s micro-organisms also synthesizes 90% of the serotonin in our bodies, which is essential for the stability of our metabolism (homostatis), platelet aggregation, immune responses, bone development, and cardiac function. In addition, the gut’s microbiome produces neurochemicals, like dopamine and norepinephrine, in large enough quantities that it affects our neurophysiology.

The human microbiome is so interwoven into our metabolism, immune system and cognitive processes, that it is now believe that humans and their microbiome evolved together. As we evolved so did our microbiome and vice versa. One modern example of this co-evolution is the variation of the GI microbiomes in those who follow a western diet versus those who don’t. Westerners have 15-30% fewer species in their guts than non-Westerners. This follows the pattern seen in both non-human primates and pre-agricultural humans who both have more species in their microbiomes than modern humans do. As our diet has shifted and we’ve started cooking our food, the number of species of microbiota in our gut has shrunk.

At a basic level, all plants and animals are the product of co-evolution with microscopic organisms. The difference between eukaryotes (plants and animals) and prokaryotes (bacteria and archaea) is that eukaryotes’ cells have organelles within them like a nucleus, chloroplast, or mitochondria. Each organelle is surrounded by a membrane and carries out various functions within the cell. But these organelles are believed to have once been separate organisms which the parent cell engulfed. And they lived happily ever after. Well, coevolved together ever after, which is probably the best you can ask for in such a close relationship. :^)

But back to us and our internal ecosystem. A healthy gut biome is known to reduce anxiety, depression, stress, and improve cognitive behavior. If we treat our GI’s microbiome right we reduce our susceptibility to cardiovascular disease, osteoporosis, obesity, asthma, heart disease, diabetes, irritable bowel disease (IBD), Parkinson's disease, cancers, Alzehimers and other forms of dementia. Indeed, some authors conclude that the microbiome may well impact on every aspect of a human body.

It’s therefore pretty important to take care of our gut’s health and that means eating a healthy diet. It’s reassuring that this is well within our control, given the bizarreness of realizing we have a rich ecosystem within our guts. While what’s best for everyone’s microbiomes is different, because we all have different genetics and history, there are a few broad rules. First off, we’re advised to avoid sugar and artificial sweeteners, to avoid saturated oils which are primarily animal and tropical oils, and to avoid red meat and excessive alcohol. And in particular, we’re warned to avoid processed foods. All of these promote the growth of bad bacteria at the expense of the good. On the do-eat side for gut health, we can include prebiotic and probiotic foods. Prebiotic foods are those which provide food for the biota in our bellies. Prebiotics are all fibers and include garlic, onions, wheat, soybeans, and oats as well as a variety of other veg and grains. Probiotic foods are those which actually contain healthy bacteria. Foods like cultured yoghurts and cottage cheese, and fermented foods like kimchi, miso, and sauerkraut are excellent sources of healthy bacteria. Probiotics, it took me five years to learn this lesson, are helpful to take when we’ve taken antibiotics. Finally, it’s important to drink plenty of water to aid the gut in its work.

When I set out to write about the mind-gut connection, I wanted to explore the idea that our gut is our second brain. While I figured this nickname had something to do with regulation of nutrients and energy flows, I had no idea that our gut is hugely important for our mood, our immune system, our resistance to cancers and obesity, and for reducing inflammation which underpins so many of our ills.

Nor did I dream that the advice for taking care of this second brain, would ricochet us right back into eco-warrior territory. But, it shouldn’t surprise me that the best way to take care of our inner ecosystem is to eat a diet that also takes care of the ecosystems around us. Eating whole foods and reducing meat and processed foods will not only improve our inner microbiome, but will also reduce our carbon footprint, our water footprint, our land footprint, and our garbage footprint. As the recognition that we are embedded in and host to other ecosystems sinks in, it becomes second nature to nurture our second brains.